diff --git a/Cargo.lock b/Cargo.lock
index 2f5903ab9..6a87905c3 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4188,6 +4188,7 @@ dependencies = [
  "objc2-core-foundation",
  "objc2-core-text",
  "serde",
+ "serde_json",
  "specta",
  "windows",
 ]
@@ -6186,6 +6187,7 @@ dependencies = [
  "objc2-app-kit 0.3.2",
  "objc2-core-foundation",
  "objc2-foundation 0.3.2",
+ "objc2-web-kit 0.3.2",
  "parking_lot",
  "serde",
  "serde_json",
diff --git a/THIRD_PARTY_LICENSES.md b/THIRD_PARTY_LICENSES.md
index 9a377fecd..94751e75a 100644
--- a/THIRD_PARTY_LICENSES.md
+++ b/THIRD_PARTY_LICENSES.md
@@ -1,5 +1,13 @@
 # Third-party licenses
 
+## Project Lombok
+
+`plugins/lombok/lombok-1.18.48-openidea.1.jar` contains Project Lombok v1.18.48 with the Equinox
+classloader fix from [projectlombok/lombok#4059](https://github.com/projectlombok/lombok/pull/4059).
+Copyright (C) 2009-2021 The Project Lombok Authors. MIT license and bundled component
+notices are retained in [plugins/lombok/LICENSE](plugins/lombok/LICENSE) and inside the jar.
+Source tag, patch commits and build instructions: [plugins/lombok/README.md](plugins/lombok/README.md).
+
 ## JetBrains IntelliJ Platform icons
 
 `src/ui/expui/**` contains SVG icons from the IntelliJ Platform "new UI" (expui)
diff --git a/crates/ide-build/src/compile/fingerprint.rs b/crates/ide-build/src/compile/fingerprint.rs
new file mode 100644
index 000000000..8274003d6
--- /dev/null
+++ b/crates/ide-build/src/compile/fingerprint.rs
@@ -0,0 +1,321 @@
+//! Metadata fingerprints for successful Maven launch builds.
+use super::*;
+use std::fs;
+use std::hash::{Hash, Hasher};
+use std::time::SystemTime;
+
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub struct LaunchFingerprint {
+    version: u32,
+    parameters: String,
+    files: BTreeMap<PathBuf, Option<(u64, SystemTime)>>,
+}
+
+fn scan(
+    path: &Path,
+    files: &mut BTreeMap<PathBuf, Option<(u64, SystemTime)>>,
+    ancestors: &mut HashSet<PathBuf>,
+    cancel: &CancellationToken,
+) -> IdeResult<()> {
+    if cancel.is_cancelled() {
+        return Err(IdeError::cancelled());
+    }
+    let meta = match fs::metadata(path) {
+        Ok(meta) => meta,
+        Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
+            files.insert(path.to_path_buf(), None);
+            return Ok(());
+        }
+        Err(e) => return Err(e.into()),
+    };
+    if meta.is_dir() {
+        let canonical = dunce::canonicalize(path)?;
+        if !ancestors.insert(canonical.clone()) {
+            return Err(IdeError::internal("cyclic launch input directory"));
+        }
+        // Directory mtimes change on irrelevant JDT writes. File paths detect additions/deletions.
+        files.insert(path.to_path_buf(), None);
+        for entry in fs::read_dir(path)? {
+            scan(&entry?.path(), files, ancestors, cancel)?;
+        }
+        ancestors.remove(&canonical);
+    } else if meta.is_file() {
+        files.insert(path.to_path_buf(), Some((meta.len(), meta.modified()?)));
+    } else {
+        return Err(IdeError::internal("unsupported launch input file"));
+    }
+    Ok(())
+}
+
+/// `None` means an input cannot be resolved safely: build normally without reuse.
+/// All filesystem work belongs on the caller's blocking thread.
+pub fn launch_fingerprint(
+    root: &Path,
+    model: &BuildModel,
+    module: &Path,
+    test: bool,
+    local_repo: Option<PathBuf>,
+    cancel: &CancellationToken,
+) -> IdeResult<Option<LaunchFingerprint>> {
+    let Some(m) = &model.maven else { return Ok(None) };
+    let projects = maven_launch_projects(root, m, module, test);
+    if projects.is_empty() {
+        return Ok(None);
+    }
+    let Some(mut inputs) = maven::launch_inputs(root, &projects, local_repo) else { return Ok(None) };
+    let plan = launch_plan(root, model, module, test)?;
+    let mut environment: BTreeMap<String, String> = std::env::vars()
+        .map(|(key, value)| (key.to_ascii_uppercase(), value))
+        .filter(|(key, _)| {
+            key.starts_with("MAVEN_")
+                || key.starts_with("JAVA_")
+                || key.starts_with("JDK_")
+                || matches!(
+                    key.as_str(),
+                    "PATH" | "HOME" | "LANG" | "LC_ALL" | "_JAVA_OPTIONS" | "M2_HOME" | "MAVEN_HOME"
+                )
+        })
+        .collect();
+    // Explicit step values override the inherited environment just as they do in Command.
+    for step in &plan.steps {
+        environment.extend(step.env.iter().map(|(key, value)| (key.to_ascii_uppercase(), value.clone())));
+        for dir in step.cwd.ancestors() {
+            inputs.extend([dir.join(".mvn"), dir.join("mvnw"), dir.join("mvnw.cmd")]);
+            if dir == root {
+                break;
+            }
+        }
+        let program = process::program_path(&step.program, &step.env);
+        inputs.push(program.clone());
+        // Maven installed via a symlink still reads conf from its distribution.
+        if let Ok(program) = dunce::canonicalize(program)
+            && let Some(home) = program.parent().and_then(Path::parent)
+        {
+            for conf in ["conf", "libexec/conf"] {
+                inputs.extend([home.join(conf).join("settings.xml"), home.join(conf).join("toolchains.xml")]);
+            }
+        }
+        if !environment.contains_key("JAVA_HOME") {
+            let java = process::program_path(if cfg!(windows) { "java.exe" } else { "java" }, &step.env);
+            inputs.push(java.clone());
+            if let Ok(java) = dunce::canonicalize(java)
+                && let Some(home) = java.parent().and_then(Path::parent)
+            {
+                inputs.push(home.join("release"));
+            }
+        }
+        for (i, arg) in step.args.iter().enumerate() {
+            if matches!(arg.as_str(), "-s" | "--settings" | "-gs" | "--global-settings" | "-t" | "--toolchains")
+                && let Some(file) = step.args.get(i + 1)
+            {
+                inputs.push(step.cwd.join(file));
+            }
+            for prefix in ["--settings=", "--global-settings=", "--toolchains="] {
+                if let Some(file) = arg.strip_prefix(prefix) {
+                    inputs.push(step.cwd.join(file));
+                }
+            }
+        }
+    }
+    if let Some(home) = dirs::home_dir() {
+        inputs.extend([home.join(".m2/settings.xml"), home.join(".m2/toolchains.xml")]);
+    }
+    for key in ["MAVEN_HOME", "M2_HOME"] {
+        if let Some(home) = environment.get(key) {
+            inputs.extend([Path::new(home).join("conf/settings.xml"), Path::new(home).join("conf/toolchains.xml")]);
+        }
+    }
+    if let Some(home) = environment.get("JAVA_HOME") {
+        inputs.extend([
+            Path::new(home).join("release"),
+            Path::new(home).join("lib/modules"),
+            Path::new(home).join("lib/tools.jar"),
+            Path::new(home).join(if cfg!(windows) { "bin/java.exe" } else { "bin/java" }),
+        ]);
+    }
+    let steps: Vec<_> =
+        plan.steps.iter().map(|s| (process::program_path(&s.program, &s.env), &s.args, &s.cwd, &s.env)).collect();
+    // Profiles and plugins can read arbitrary environment variables. Keep a signature
+    // of the inherited environment without persisting unrelated credentials.
+    let inherited: BTreeMap<_, _> = std::env::vars_os().collect();
+    let mut inherited_hash = std::hash::DefaultHasher::new();
+    inherited.hash(&mut inherited_hash);
+    let parameters =
+        serde_json::to_string(&(root, module, test, steps, environment, inherited_hash.finish(), projects))
+            .map_err(|e| IdeError::internal(e.to_string()))?;
+    let mut files = BTreeMap::new();
+    for path in inputs {
+        scan(&path, &mut files, &mut HashSet::new(), cancel)?;
+    }
+    // Store project inputs relative to the project, including each file's relative path.
+    let files = files.into_iter().map(|(p, stamp)| (p.strip_prefix(root).unwrap_or(&p).to_path_buf(), stamp)).collect();
+    Ok(Some(LaunchFingerprint { version: 1, parameters, files }))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn write(root: &Path, rel: &str, value: &str) {
+        let path = root.join(rel);
+        fs::create_dir_all(path.parent().unwrap()).unwrap();
+        fs::write(path, value).unwrap();
+    }
+
+    fn fixture(root: &Path) -> BuildModel {
+        write(
+            root,
+            "pom.xml",
+            r#"<project><groupId>demo</groupId><artifactId>parent</artifactId><version>1</version>
+            <packaging>pom</packaging><modules><module>lib</module><module>app</module></modules></project>"#,
+        );
+        write(
+            root,
+            "lib/pom.xml",
+            r#"<project><parent><groupId>demo</groupId><artifactId>parent</artifactId><version>1</version></parent>
+            <artifactId>lib</artifactId><build><sourceDirectory>code</sourceDirectory><resources><resource><directory>conf</directory></resource></resources></build></project>"#,
+        );
+        write(
+            root,
+            "app/pom.xml",
+            r#"<project><parent><groupId>demo</groupId><artifactId>parent</artifactId><version>1</version></parent>
+            <artifactId>app</artifactId><dependencies><dependency><groupId>demo</groupId><artifactId>lib</artifactId><version>1</version></dependency></dependencies></project>"#,
+        );
+        write(root, "lib/src/main/kotlin/Channel.kt", "value");
+        write(root, "app/src/main/resources/app.properties", "key=value");
+        write(root, "lib/conf/custom.properties", "custom=value");
+        write(root, "lib/code/Custom.java", "class Custom {}");
+        BuildModel { maven: Some(maven::load(root)), ..Default::default() }
+    }
+
+    fn fingerprint(root: &Path, model: &BuildModel) -> Option<LaunchFingerprint> {
+        launch_fingerprint(root, model, &root.join("app"), false, None, &CancellationToken::new()).unwrap()
+    }
+
+    #[test]
+    fn unchanged_inputs_match_but_source_resource_pom_add_delete_and_mtime_invalidate() {
+        for rel in [
+            "lib/src/main/kotlin/Channel.kt",
+            "app/src/main/resources/app.properties",
+            "lib/conf/custom.properties",
+            "lib/code/Custom.java",
+            "app/pom.xml",
+            "lib/pom.xml",
+            "pom.xml",
+            ".mvn/maven.config",
+            "lib/src/main/groovy/New.groovy",
+            "app/src/test/scala/Test.scala",
+        ] {
+            let dir = tempfile::tempdir().unwrap();
+            let root = dir.path();
+            let model = fixture(root);
+            let before = fingerprint(root, &model);
+            assert!(before.is_some());
+            assert_eq!(before, fingerprint(root, &model), "unchanged {rel}");
+            let serialized = serde_json::to_vec(&before).unwrap();
+            assert_eq!(before, serde_json::from_slice(&serialized).unwrap());
+            let value = if rel.ends_with("pom.xml") {
+                format!("{}<!-- changed -->", fs::read_to_string(root.join(rel)).unwrap())
+            } else {
+                "changed input".to_owned()
+            };
+            write(root, rel, &value);
+            let changed = fingerprint(root, &model);
+            assert_ne!(before, changed, "changed/added {rel}");
+            let file = fs::OpenOptions::new().write(true).open(root.join(rel)).unwrap();
+            file.set_modified(SystemTime::UNIX_EPOCH + std::time::Duration::from_secs(42)).unwrap();
+            let touched = fingerprint(root, &model);
+            assert_ne!(changed, touched, "mtime-only {rel}");
+            fs::remove_file(root.join(rel)).unwrap();
+            assert_ne!(touched, fingerprint(root, &model), "deleted {rel}");
+        }
+    }
+
+    #[test]
+    fn profile_options_jdk_goal_and_wrapper_invalidate_without_using_class_outputs() {
+        let dir = tempfile::tempdir().unwrap();
+        let root = dir.path();
+        let mut model = fixture(root);
+        let before = fingerprint(root, &model);
+        write(root, "lib/target/classes/Channel.class", "JDT stub");
+        write(root, "app/target/classes/Main.class", "JDT stub");
+        assert_eq!(before, fingerprint(root, &model));
+        let mut previous = before.clone();
+        for option in ["-Pdev", "-Pprod", "-DskipTests", "-o"] {
+            model.maven.as_mut().unwrap().projects[0].options = vec![option.into()];
+            let current = fingerprint(root, &model);
+            assert_ne!(previous, current, "{option}");
+            previous = current;
+        }
+        model.maven.as_mut().unwrap().projects[0].options.clear();
+        model.maven.as_mut().unwrap().projects[0]
+            .env
+            .insert("JAVA_HOME".into(), root.join("jdk").to_string_lossy().into_owned());
+        let jdk = fingerprint(root, &model);
+        assert_ne!(before, jdk);
+        write(root, "jdk/release", "JAVA_VERSION=21");
+        assert_ne!(jdk, fingerprint(root, &model));
+        model.maven.as_mut().unwrap().projects[0].env.clear();
+        let test = launch_fingerprint(root, &model, &root.join("app"), true, None, &CancellationToken::new())
+            .unwrap()
+            .unwrap();
+        assert_ne!(before, Some(test));
+        write(root, "mvnw", "wrapper changed");
+        assert_ne!(before, fingerprint(root, &model));
+    }
+
+    #[test]
+    fn unresolved_roots_and_cancel_never_claim_up_to_date() {
+        let dir = tempfile::tempdir().unwrap();
+        let root = dir.path();
+        let model = fixture(root);
+        write(
+            root,
+            "lib/pom.xml",
+            "<project><artifactId>lib</artifactId><build><sourceDirectory>${unknown}/src</sourceDirectory></build></project>",
+        );
+        assert!(
+            launch_fingerprint(root, &model, &root.join("app"), false, None, &CancellationToken::new())
+                .unwrap()
+                .is_none()
+        );
+        let model = fixture(root);
+        let cancel = CancellationToken::new();
+        cancel.cancel();
+        assert!(launch_fingerprint(root, &model, &root.join("app"), false, None, &cancel).is_err());
+    }
+    #[test]
+    fn external_parent_and_selected_settings_files_invalidate() {
+        let dir = tempfile::tempdir().unwrap();
+        let root = dir.path().join("project");
+        let repo = dir.path().join("repository");
+        write(
+            &repo,
+            "demo/parent/1/parent-1.pom",
+            "<project><groupId>demo</groupId><artifactId>parent</artifactId><version>1</version></project>",
+        );
+        write(
+            &root,
+            "pom.xml",
+            "<project><parent><groupId>demo</groupId><artifactId>parent</artifactId><version>1</version><relativePath/></parent><artifactId>app</artifactId></project>",
+        );
+        let mut model = crate::load(&root, &root.join("cache"), Some(repo.clone()));
+        let settings = dir.path().join("custom-settings.xml");
+        fs::write(&settings, "<settings/>").unwrap();
+        model.maven.as_mut().unwrap().projects[0].options = vec!["-s".into(), settings.to_string_lossy().into_owned()];
+        let get =
+            || launch_fingerprint(&root, &model, &root, false, Some(repo.clone()), &CancellationToken::new()).unwrap();
+        let before = get();
+        assert!(before.is_some());
+        write(
+            &repo,
+            "demo/parent/1/parent-1.pom",
+            "<project><groupId>demo</groupId><artifactId>parent</artifactId><version>1</version><!-- changed --></project>",
+        );
+        let parent = get();
+        assert_ne!(before, parent);
+        fs::write(settings, "<settings><activeProfiles><activeProfile>dev</activeProfile></activeProfiles></settings>")
+            .unwrap();
+        assert_ne!(parent, get());
+    }
+}
diff --git a/crates/ide-build/src/compile/mod.rs b/crates/ide-build/src/compile/mod.rs
index 857912ada..9cd0ea26f 100644
--- a/crates/ide-build/src/compile/mod.rs
+++ b/crates/ide-build/src/compile/mod.rs
@@ -3,8 +3,11 @@
 //! background with cancellation and parses the compiler output into messages
 //! for the Build tool window, the Problems view and the editor.
 
+mod fingerprint;
 mod parse;
 
+pub use fingerprint::{LaunchFingerprint, launch_fingerprint};
+
 use crate::process::{self, Stream};
 use crate::{BuildModel, maven};
 use ide_core::{CancellationToken, Diagnostic, IdeError, IdeResult, Pos, Range, Severity};
@@ -237,12 +240,7 @@ fn maven_steps(root: &Path, model: &BuildModel, kind: BuildKind, module: Option<
     if !m.projects.iter().any(|p| p.dir == rel) {
         return Err(IdeError::not_found("no linked Maven project found for module"));
     }
-    let top = tops
-        .iter()
-        .filter(|t| t.dir.is_empty() || rel == t.dir || rel.starts_with(&format!("{}/", t.dir)))
-        .max_by_key(|t| t.dir.len())
-        .copied()
-        .unwrap_or(tops[0]);
+    let top = maven_reactor(m, &rel).ok_or_else(|| IdeError::not_found("no linked Maven project found for module"))?;
     let top_dir = subdir(root, &top.dir);
     if module == top_dir {
         return Ok(vec![step(top, &[])]);
@@ -611,6 +609,90 @@ pub fn has_non_java_sources(module: &Path) -> bool {
     walk(&module.join("src"), 12)
 }
 
+fn reactor_projects<'a>(m: &'a maven::MavenModel, top: &'a maven::MavenProject) -> Vec<&'a maven::MavenProject> {
+    let mut projects = Vec::new();
+    let mut pending = vec![top];
+    let mut seen = HashSet::new();
+    while let Some(p) = pending.pop() {
+        if !seen.insert(&p.pom) {
+            continue;
+        }
+        projects.push(p);
+        pending.extend(m.projects.iter().filter(|child| p.modules.contains(&child.pom)));
+    }
+    projects
+}
+
+fn maven_reactor<'a>(m: &'a maven::MavenModel, module: &str) -> Option<&'a maven::MavenProject> {
+    m.projects.iter().filter(|p| !p.aggregated).find(|top| reactor_projects(m, top).iter().any(|p| p.dir == module))
+}
+
+/// Launch module first, followed by its upstream modules in the same Maven reactor.
+/// External artifacts and unrelated linked reactors are never rebuilt for this launch.
+fn maven_launch_projects<'a>(
+    root: &Path,
+    m: &'a maven::MavenModel,
+    module: &Path,
+    test: bool,
+) -> Vec<&'a maven::MavenProject> {
+    let rel = rel_str(root, module);
+    let Some(top) = maven_reactor(m, &rel) else { return Vec::new() };
+    let reactor = reactor_projects(m, top);
+    let Some(start) = reactor.iter().find(|p| p.dir == rel) else { return Vec::new() };
+    let mut pending = vec![*start];
+    let mut seen = HashSet::new();
+    let mut projects = Vec::new();
+    while let Some(p) = pending.pop() {
+        if !seen.insert(&p.pom) {
+            continue;
+        }
+        projects.push(p);
+        for dep in &p.dependencies {
+            if !dep.resolved() || (dep.scope == "test" && (!test || p.pom != start.pom)) {
+                continue;
+            }
+            if let Some(upstream) = reactor.iter().find(|u| {
+                u.group_id == dep.group_id
+                    && u.artifact_id == dep.artifact_id
+                    && dep.version.as_ref().is_none_or(|v| *v == u.version)
+            }) {
+                pending.push(*upstream);
+            }
+        }
+    }
+    projects
+}
+
+/// Whether a launch requires the external JVM compiler. Maven includes upstream
+/// reactor dependencies; adapter selection remains a separate, module-local decision.
+pub fn launch_has_non_java_sources(root: &Path, model: &BuildModel, module: &Path, test: bool) -> bool {
+    if let Some(m) = &model.maven {
+        let projects = maven_launch_projects(root, m, module, test);
+        if !projects.is_empty() {
+            return projects.iter().any(|p| has_non_java_sources(&subdir(root, &p.dir)));
+        }
+    }
+    has_non_java_sources(module)
+}
+
+fn launch_plan(root: &Path, model: &BuildModel, module: &Path, test: bool) -> IdeResult<BuildPlan> {
+    let kind = if model.maven.as_ref().is_some_and(|m| m.projects.iter().any(|p| subdir(root, &p.dir) == module)) {
+        // JDT may have left newer error stubs in Maven's output directories.
+        BuildKind::Rebuild
+    } else {
+        BuildKind::Build
+    };
+    let mut plan = plan(root, model, kind, Some(module))?;
+    if plan.system == BuildSystem::Maven && !test {
+        for step in &mut plan.steps {
+            if let Some(goal) = step.args.last_mut() {
+                *goal = "compile".into();
+            }
+        }
+    }
+    Ok(plan)
+}
+
 /// Compiles the module at `module` with its build system before a JVM launch and
 /// returns the class directories it wrote, to put ahead of the jdtls classpath.
 pub fn build_for_launch(
@@ -620,7 +702,7 @@ pub fn build_for_launch(
     test: bool,
     cancel: &CancellationToken,
 ) -> IdeResult<Vec<PathBuf>> {
-    let plan = plan(root, model, BuildKind::Build, Some(module))?;
+    let plan = launch_plan(root, model, module, test)?;
     let result = run(root, &plan, cancel, &|_| {})?;
     if !result.success {
         let errors: Vec<String> = result
@@ -635,6 +717,14 @@ pub fn build_for_launch(
             .collect();
         return Err(IdeError::internal(format!("Build failed:\n{}", errors.join("\n"))));
     }
+    if plan.system == BuildSystem::Maven
+        && let Some(m) = &model.maven
+    {
+        return Ok(maven_launch_projects(root, m, module, test)
+            .iter()
+            .flat_map(|p| launch_class_dirs(plan.system, &subdir(root, &p.dir), test && subdir(root, &p.dir) == module))
+            .collect());
+    }
     Ok(launch_class_dirs(plan.system, module, test))
 }
 
@@ -821,6 +911,142 @@ mod tests {
         }
     }
 
+    fn reactor_model() -> BuildModel {
+        let project = |dir: &str, deps: &[&str]| maven::MavenProject {
+            pom: format!("{dir}/pom.xml"),
+            dir: dir.into(),
+            group_id: "probe".into(),
+            artifact_id: dir.into(),
+            version: "1".into(),
+            aggregated: true,
+            dependencies: deps
+                .iter()
+                .map(|d| maven::MavenDependency {
+                    group_id: "probe".into(),
+                    artifact_id: (*d).into(),
+                    version: Some("1".into()),
+                    scope: "compile".into(),
+                    ..Default::default()
+                })
+                .collect(),
+            ..Default::default()
+        };
+        let mut projects = vec![
+            project("app", &["middle"]),
+            project("middle", &["lib"]),
+            project("lib", &["app"]),
+            project("unrelated", &[]),
+        ];
+        projects.insert(
+            0,
+            maven::MavenProject {
+                pom: "pom.xml".into(),
+                artifact_id: "reactor".into(),
+                command: "mvnw".into(),
+                modules: projects.iter().map(|p| p.pom.clone()).collect(),
+                options: vec!["-s".into(), "settings.xml".into()],
+                env: BTreeMap::from([("JAVA_HOME".into(), "/jdk".into())]),
+                ..Default::default()
+            },
+        );
+        BuildModel { maven: Some(maven::MavenModel { projects, ..Default::default() }), ..Default::default() }
+    }
+
+    #[test]
+    fn mixed_launch_detection_follows_only_reactor_dependencies() {
+        for extension in ["kt", "groovy", "scala"] {
+            let tmp = tempfile::tempdir().unwrap();
+            let root = tmp.path();
+            let mut model = reactor_model();
+            write(root, "app/src/main/java/Application.java", "class Application {}");
+            write(root, &format!("unrelated/src/main/java/Other.{extension}"), "");
+            assert!(!launch_has_non_java_sources(root, &model, &root.join("app"), false));
+            write(root, &format!("lib/src/main/java/Channel.{extension}"), "");
+            assert!(launch_has_non_java_sources(root, &model, &root.join("app"), false));
+            assert_eq!(
+                maven_launch_projects(root, model.maven.as_ref().unwrap(), &root.join("app"), false).len(),
+                3,
+                "cycles terminate"
+            );
+            let m = model.maven.as_mut().unwrap();
+            m.projects[2].dependencies[0].scope = "test".into();
+            assert!(
+                !launch_has_non_java_sources(root, &model, &root.join("app"), true),
+                "upstream test dependencies are not transitive"
+            );
+            let m = model.maven.as_mut().unwrap();
+            m.projects[1].dependencies[0].scope = "test".into();
+            m.projects[2].dependencies[0].scope = "compile".into();
+            assert!(!launch_has_non_java_sources(root, &model, &root.join("app"), false));
+            assert!(launch_has_non_java_sources(root, &model, &root.join("app"), true));
+            model.maven.as_mut().unwrap().projects[2].dependencies[0].version = Some("external".into());
+            assert!(!launch_has_non_java_sources(root, &model, &root.join("app"), true));
+            model.maven.as_mut().unwrap().projects[2].dependencies[0].version = Some("1".into());
+            model.maven.as_mut().unwrap().projects[3].aggregated = false;
+            model.maven.as_mut().unwrap().projects[0].modules.retain(|p| p != "lib/pom.xml");
+            assert!(
+                !launch_has_non_java_sources(root, &model, &root.join("app"), true),
+                "another linked reactor is external"
+            );
+        }
+    }
+
+    #[test]
+    fn maven_launch_steps_use_reactor_settings_and_launch_scope() {
+        let tmp = tempfile::tempdir().unwrap();
+        let root = tmp.path();
+        write(root, "app/pom.xml", "<project/>");
+        let model = reactor_model();
+        for (test, goal) in [(false, "compile"), (true, "test-compile")] {
+            let plan = launch_plan(root, &model, &root.join("app"), test).unwrap();
+            let step = &plan.steps[0];
+            assert_eq!(step.cwd, root);
+            assert_eq!(step.program, "mvnw");
+            assert_eq!(step.env["JAVA_HOME"], "/jdk");
+            assert_eq!(
+                step.args,
+                ["-B", "-Dstyle.color=never", "-s", "settings.xml", "-pl", "app", "-am", "clean", goal]
+            );
+        }
+    }
+
+    #[cfg(unix)]
+    #[test]
+    fn external_launch_returns_upstream_outputs_and_blocks_failure_or_cancellation() {
+        use std::os::unix::fs::PermissionsExt;
+        let tmp = tempfile::tempdir().unwrap();
+        let root = tmp.path();
+        write(root, "app/pom.xml", "<project/>");
+        write(
+            root,
+            "mvnw",
+            "#!/bin/sh\nmkdir -p app/target/classes middle/target/classes lib/target/classes app/target/test-classes\n",
+        );
+        let wrapper = root.join("mvnw");
+        std::fs::set_permissions(&wrapper, std::fs::Permissions::from_mode(0o755)).unwrap();
+        let mut model = reactor_model();
+        model.maven.as_mut().unwrap().projects[0].command = wrapper.to_string_lossy().into_owned();
+        let dirs = build_for_launch(root, &model, &root.join("app"), true, &CancellationToken::new()).unwrap();
+        assert_eq!(
+            dirs,
+            ["app/target/test-classes", "app/target/classes", "middle/target/classes", "lib/target/classes"]
+                .map(|p| root.join(p))
+        );
+        write(
+            root,
+            "mvnw",
+            "#!/bin/sh\necho '[ERROR] Kotlin compilation failed: unresolved reference broken' >&2\nexit 1\n",
+        );
+        let error = build_for_launch(root, &model, &root.join("app"), false, &CancellationToken::new()).unwrap_err();
+        assert!(error.message.contains("Kotlin compilation failed"), "{}", error.message);
+        let cancel = CancellationToken::new();
+        cancel.cancel();
+        assert_eq!(
+            build_for_launch(root, &model, &root.join("app"), false, &cancel).unwrap_err().kind,
+            ide_core::error::ErrorKind::Cancelled
+        );
+    }
+
     #[test]
     fn non_java_launch_class_dirs() {
         let tmp = tempfile::tempdir().unwrap();
diff --git a/crates/ide-build/src/kotlin_bridge.rs b/crates/ide-build/src/kotlin_bridge.rs
new file mode 100644
index 000000000..150170efc
--- /dev/null
+++ b/crates/ide-build/src/kotlin_bridge.rs
@@ -0,0 +1,475 @@
+//! Private Maven builds for JDT's Kotlin binary libraries. Never use launch outputs.
+
+use crate::BuildModel;
+use crate::compile::{self, BuildEvent, BuildKind, BuildMessage};
+use ide_core::{CancellationToken, IdeError, IdeResult};
+use serde::{Deserialize, Serialize};
+use std::collections::BTreeMap;
+use std::path::{Path, PathBuf};
+
+#[derive(Clone, Debug, Deserialize)]
+#[serde(rename_all = "camelCase")]
+struct Module {
+    key: String,
+    project_uri: String,
+    output: PathBuf,
+    test_output: Option<PathBuf>,
+    dependencies: Vec<Dependency>,
+    has_kotlin: bool,
+    kotlin_goals: Vec<KotlinGoal>,
+}
+
+#[derive(Clone, Debug, Deserialize)]
+struct KotlinGoal {
+    execution: String,
+    status: String,
+}
+
+#[derive(Clone, Debug, Deserialize)]
+struct Dependency {
+    key: String,
+    scope: String,
+    #[serde(rename = "type")]
+    kind: Option<String>,
+    classifier: Option<String>,
+}
+
+#[derive(Clone, Debug, Serialize, PartialEq, Eq)]
+pub struct Library {
+    pub path: PathBuf,
+    pub test: bool,
+}
+
+#[derive(Clone, Debug, Serialize, PartialEq, Eq)]
+#[serde(rename_all = "camelCase")]
+pub struct ProjectLibraries {
+    pub project_uri: String,
+    pub libraries: Vec<Library>,
+}
+
+pub struct Outcome {
+    pub projects: Vec<ProjectLibraries>,
+    pub messages: Vec<BuildMessage>,
+    pub success: bool,
+}
+
+/// Inspect sources, excluding generated/build/VCS trees and never following symlinks.
+pub fn has_kotlin(root: &Path) -> bool {
+    let Ok(entries) = std::fs::read_dir(root) else { return false };
+    entries.flatten().any(|entry| {
+        let Ok(kind) = entry.file_type() else { return false };
+        if kind.is_file() {
+            entry.path().extension().is_some_and(|e| e == "kt")
+        } else {
+            kind.is_dir()
+                && !matches!(
+                    entry.file_name().to_str(),
+                    Some("target" | "build" | "out" | "bin" | "node_modules" | ".git" | ".openidea")
+                )
+                && has_kotlin(&entry.path())
+        }
+    })
+}
+
+/// Run the project's configured wrapper/settings/JDK and lifecycle, with an output
+/// redirector loaded before Maven calculates its lifecycle execution plans.
+pub fn build(
+    root: &Path,
+    model: &BuildModel,
+    bundle: &Path,
+    generation: &Path,
+    cancel: &CancellationToken,
+) -> IdeResult<Outcome> {
+    std::fs::create_dir_all(generation)?;
+    let mut plan = compile::plan(root, model, BuildKind::Build, None)?;
+    if plan.system != compile::BuildSystem::Maven {
+        return Err(IdeError::invalid("Kotlin bridge requires a Maven build root"));
+    }
+    let mut manifests = Vec::new();
+    for (index, step) in plan.steps.iter_mut().enumerate() {
+        step.args.push("--fail-at-end".into());
+        let directory = generation.join(format!("reactor-{index}"));
+        std::fs::create_dir_all(&directory)?;
+        manifests.push(directory.join("modules.json"));
+        let mut extensions = vec![bundle.to_path_buf()];
+        step.args.retain(|arg| {
+            if let Some(value) = arg.strip_prefix("-Dmaven.ext.class.path=") {
+                extensions.extend(std::env::split_paths(value));
+                false
+            } else {
+                true
+            }
+        });
+        let extension_path = std::env::join_paths(extensions).map_err(|e| IdeError::invalid(e.to_string()))?;
+        step.args.push(format!("-Dmaven.ext.class.path={}", extension_path.to_string_lossy()));
+        step.args.push(format!("-Dopenidea.kotlin.staging={}", directory.join("staging").display()));
+    }
+    let mut messages = Vec::new();
+    // Independent linked reactors must still run after another reactor's javac fails.
+    for step in &plan.steps {
+        let mut reactor = plan.clone();
+        reactor.steps = vec![step.clone()];
+        let result = compile::run(root, &reactor, cancel, &|event| {
+            if let BuildEvent::Output { text, .. } = event {
+                tracing::debug!("kotlin bridge: {}", text.trim_end());
+            }
+        })?;
+        messages.extend(result.messages);
+    }
+    // javac diagnostics belong to JDT, including when a Kotlin target was skipped.
+    messages.retain(|message| {
+        message.path.as_ref().is_some_and(|path| PathBuf::from(path.clone()).extension().is_some_and(|e| e == "kt"))
+    });
+    let mut modules = Vec::new();
+    for manifest in manifests {
+        let parsed: Vec<Module> = serde_json::from_slice(&std::fs::read(manifest)?)
+            .map_err(|e| IdeError::internal(format!("Kotlin module manifest: {e}")))?;
+        modules.extend(parsed);
+    }
+    messages.extend(kotlin_failures(&modules));
+    if messages.iter().any(|message| message.severity == ide_core::Severity::Error) {
+        return Ok(Outcome { projects: Vec::new(), messages, success: false });
+    }
+    let pending = generation.join("libraries.pending");
+    let published = generation.join("libraries");
+    std::fs::create_dir_all(&pending)?;
+    let mut libraries = BTreeMap::new();
+    for (index, module) in modules.iter().enumerate() {
+        let mut outputs = ModuleLibraries::default();
+        for (source, target, name) in [
+            (Some(&module.output), &mut outputs.main, format!("main-{index}")),
+            (module.test_output.as_ref(), &mut outputs.test, format!("test-{index}")),
+        ] {
+            let Some(source) = source else { continue };
+            if !source.starts_with(generation) {
+                return Err(IdeError::internal("Kotlin build output escaped staging"));
+            }
+            if copy_kotlin(source, &pending.join(&name), cancel)? {
+                *target = Some(published.join(name));
+            }
+        }
+        libraries.insert(module.key.clone(), outputs);
+    }
+    publish(&pending, &published, cancel)?;
+    Ok(Outcome { projects: consumers(&modules, &libraries), messages, success: true })
+}
+
+fn kotlin_failures(modules: &[Module]) -> Vec<BuildMessage> {
+    let mut messages = Vec::new();
+    for module in modules {
+        if !module.has_kotlin {
+            continue;
+        }
+        if module.kotlin_goals.is_empty() {
+            messages.push(kotlin_failure(module, "compile target was not executed"));
+        }
+        for goal in &module.kotlin_goals {
+            if goal.status != "success" {
+                messages.push(kotlin_failure(module, &format!("{} {}", goal.execution, goal.status)));
+            }
+        }
+    }
+    messages
+}
+
+fn kotlin_failure(module: &Module, reason: &str) -> BuildMessage {
+    BuildMessage {
+        severity: ide_core::Severity::Error,
+        text: format!("Kotlin compilation for {}: {reason}", module.key),
+        path: None,
+        range: None,
+        code: None,
+    }
+}
+
+fn publish(pending: &Path, published: &Path, cancel: &CancellationToken) -> IdeResult<()> {
+    if cancel.is_cancelled() {
+        return Err(IdeError::cancelled());
+    }
+    std::fs::rename(pending, published)?;
+    Ok(())
+}
+
+#[derive(Default)]
+struct ModuleLibraries {
+    main: Option<PathBuf>,
+    test: Option<PathBuf>,
+}
+
+fn consumers(modules: &[Module], libraries: &BTreeMap<String, ModuleLibraries>) -> Vec<ProjectLibraries> {
+    modules
+        .iter()
+        .map(|consumer| {
+            let mut visible = Vec::<Library>::new();
+            let mut add = |path: &Option<PathBuf>, test: bool| {
+                if let Some(path) = path {
+                    if let Some(previous) = visible.iter_mut().find(|entry| &entry.path == path) {
+                        previous.test &= test;
+                    } else {
+                        visible.push(Library { path: path.clone(), test });
+                    }
+                }
+            };
+            if let Some(own) = libraries.get(&consumer.key) {
+                add(&own.test, true);
+                add(&own.main, false);
+            }
+            // Maven's resolved artifacts already apply exclusions, mediation and optional
+            // propagation. Preserve their classpath order, after the module's own output.
+            for dependency in &consumer.dependencies {
+                let Some(output) = libraries.get(&dependency.key) else { continue };
+                let test = match dependency.scope.as_str() {
+                    "compile" | "provided" | "system" | "" => false,
+                    "test" | "runtime" => true,
+                    _ => continue,
+                };
+                match (dependency.kind.as_deref(), dependency.classifier.as_deref()) {
+                    (Some("test-jar"), None | Some("tests")) | (Some("jar"), Some("tests")) => add(&output.test, test),
+                    (None | Some("jar"), None | Some("")) => add(&output.main, test),
+                    _ => {}
+                }
+            }
+            ProjectLibraries { project_uri: consumer.project_uri.clone(), libraries: visible }
+        })
+        .collect()
+}
+
+fn copy_kotlin(source: &Path, destination: &Path, cancel: &CancellationToken) -> IdeResult<bool> {
+    let Ok(entries) = std::fs::read_dir(source) else { return Ok(false) };
+    let mut found = false;
+    for entry in entries {
+        if cancel.is_cancelled() {
+            return Err(IdeError::cancelled());
+        }
+        let entry = entry?;
+        let kind = entry.file_type()?;
+        let path = entry.path();
+        let output = destination.join(entry.file_name());
+        if kind.is_dir() {
+            found |= copy_kotlin(&path, &output, cancel)?;
+        } else if kind.is_file() {
+            let bytes = std::fs::read(&path)?;
+            let class = path.extension().is_some_and(|e| e == "class");
+            let metadata = path.extension().is_some_and(|e| e == "kotlin_module");
+            if metadata || (class && kotlin_class(&bytes).unwrap_or(false)) {
+                std::fs::create_dir_all(destination)?;
+                std::fs::write(output, bytes)?;
+                found |= class;
+            }
+        }
+    }
+    Ok(found)
+}
+
+/// Read the actual class-level SourceFile attribute, rather than searching strings
+/// (a Java constant containing "Something.kt" must never become a Kotlin library).
+fn kotlin_class(bytes: &[u8]) -> Option<bool> {
+    struct Reader<'a> {
+        bytes: &'a [u8],
+        pos: usize,
+    }
+    impl<'a> Reader<'a> {
+        fn take(&mut self, count: usize) -> Option<&'a [u8]> {
+            let value = self.bytes.get(self.pos..self.pos.checked_add(count)?)?;
+            self.pos += count;
+            Some(value)
+        }
+        fn u2(&mut self) -> Option<usize> {
+            Some(u16::from_be_bytes(self.take(2)?.try_into().ok()?) as usize)
+        }
+        fn u4(&mut self) -> Option<usize> {
+            Some(u32::from_be_bytes(self.take(4)?.try_into().ok()?) as usize)
+        }
+        fn attributes(&mut self) -> Option<()> {
+            for _ in 0..self.u2()? {
+                self.u2()?;
+                let n = self.u4()?;
+                self.take(n)?;
+            }
+            Some(())
+        }
+    }
+    let mut reader = Reader { bytes, pos: 0 };
+    if reader.take(4)? != [0xca, 0xfe, 0xba, 0xbe] {
+        return None;
+    }
+    reader.take(4)?;
+    let count = reader.u2()?;
+    let mut utf8 = BTreeMap::new();
+    let mut index = 1;
+    while index < count {
+        match reader.take(1)?[0] {
+            1 => {
+                let n = reader.u2()?;
+                utf8.insert(index, reader.take(n)?);
+            }
+            3 | 4 | 9..=12 | 17 | 18 => {
+                reader.take(4)?;
+            }
+            5 | 6 => {
+                reader.take(8)?;
+                index += 1;
+            }
+            7 | 8 | 16 | 19 | 20 => {
+                reader.take(2)?;
+            }
+            15 => {
+                reader.take(3)?;
+            }
+            _ => return None,
+        }
+        index += 1;
+    }
+    reader.take(6)?;
+    let interfaces = reader.u2()?;
+    reader.take(interfaces.checked_mul(2)?)?;
+    for _ in 0..2 {
+        for _ in 0..reader.u2()? {
+            reader.take(6)?;
+            reader.attributes()?;
+        }
+    }
+    for _ in 0..reader.u2()? {
+        let name = reader.u2()?;
+        let length = reader.u4()?;
+        if utf8.get(&name).copied() == Some(b"SourceFile".as_slice()) && length == 2 {
+            let source = reader.u2()?;
+            return Some(utf8.get(&source)?.ends_with(b".kt"));
+        }
+        reader.take(length)?;
+    }
+    Some(false)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn every_kotlin_target_must_succeed_even_when_maven_fails_elsewhere() {
+        let mut modules: Vec<Module> = serde_json::from_str(r#"[
+            {"key":"lib","projectUri":"lib","output":"lib","dependencies":[],"hasKotlin":true,
+             "kotlinGoals":[{"execution":"main:compile","status":"success"},{"execution":"test:test-compile","status":"success"}]},
+            {"key":"java","projectUri":"java","output":"java","dependencies":[],"hasKotlin":false,"kotlinGoals":[]}
+        ]"#).unwrap();
+        assert!(kotlin_failures(&modules).is_empty());
+        for status in ["failed", "skipped"] {
+            modules[0].kotlin_goals[1].status = status.into();
+            let failures = kotlin_failures(&modules);
+            assert_eq!(failures.len(), 1);
+            assert!(failures[0].text.contains(&format!("test:test-compile {status}")));
+        }
+        modules[0].kotlin_goals.clear();
+        assert_eq!(kotlin_failures(&modules).len(), 1);
+        modules[0].has_kotlin = false;
+        assert!(kotlin_failures(&modules).is_empty());
+        assert!(
+            serde_json::from_str::<Vec<Module>>(
+                r#"[{"key":"old","projectUri":"old","output":"old","dependencies":[]}]"#
+            )
+            .is_err()
+        );
+    }
+
+    #[test]
+    fn respects_mavens_resolved_closure_and_scopes() {
+        let json = r#"[
+          {"key":"zapp","projectUri":"app","output":"app", "hasKotlin":false,"kotlinGoals":[],"dependencies":[{"key":"mid","scope":"compile","optional":false},{"key":"lib","scope":"compile","optional":false}]},
+          {"key":"mid","projectUri":"mid","output":"mid", "hasKotlin":false,"kotlinGoals":[],"dependencies":[
+            {"key":"lib","scope":"compile","optional":false},
+            {"key":"optional","scope":"compile","optional":true},
+            {"key":"test","scope":"test","optional":false},
+            {"key":"provided","scope":"provided","optional":false}]},
+          {"key":"lib","projectUri":"lib","output":"lib","hasKotlin":false,"kotlinGoals":[],"dependencies":[]}
+        ]"#;
+        let modules: Vec<Module> = serde_json::from_str(json).unwrap();
+        let libraries = ["zapp", "lib", "optional", "test", "provided"]
+            .into_iter()
+            .map(|key| (key.to_owned(), ModuleLibraries { main: Some(PathBuf::from(key)), test: None }))
+            .collect();
+        let result = consumers(&modules, &libraries);
+        assert_eq!(
+            result[0].libraries,
+            vec![Library { path: "zapp".into(), test: false }, Library { path: "lib".into(), test: false },]
+        );
+        assert_eq!(result[1].libraries.len(), 4);
+        assert!(result[1].libraries.iter().find(|l| l.path == Path::new("test")).unwrap().test);
+    }
+
+    #[test]
+    fn test_outputs_are_private_unless_maven_resolves_a_test_jar() {
+        let modules: Vec<Module> = serde_json::from_str(r#"[
+          {"key":"lib","projectUri":"lib","output":"lib","hasKotlin":false,"kotlinGoals":[],"dependencies":[]},
+          {"key":"app","projectUri":"app","output":"app","hasKotlin":false,"kotlinGoals":[],"dependencies":[{"key":"lib","scope":"compile","type":"jar","classifier":null}]},
+          {"key":"test-app","projectUri":"test-app","output":"app","hasKotlin":false,"kotlinGoals":[],"dependencies":[{"key":"lib","scope":"test","type":"test-jar","classifier":"tests"}]}
+        ]"#).unwrap();
+        let libraries =
+            BTreeMap::from([("lib".into(), ModuleLibraries { main: Some("main".into()), test: Some("test".into()) })]);
+        let result = consumers(&modules, &libraries);
+        assert_eq!(
+            result[0].libraries,
+            vec![Library { path: "test".into(), test: true }, Library { path: "main".into(), test: false }]
+        );
+        assert_eq!(result[1].libraries, vec![Library { path: "main".into(), test: false }]);
+        assert_eq!(result[2].libraries, vec![Library { path: "test".into(), test: true }]);
+    }
+
+    #[test]
+    fn publishes_complete_directories_and_cancellation_keeps_them_private() {
+        let directory = tempfile::tempdir().unwrap();
+        let pending = directory.path().join("pending");
+        let final_path = directory.path().join("published");
+        std::fs::create_dir(&pending).unwrap();
+        std::fs::write(pending.join("Channel.class"), "complete").unwrap();
+        let cancelled = CancellationToken::new();
+        cancelled.cancel();
+        assert!(publish(&pending, &final_path, &cancelled).is_err());
+        assert!(!final_path.exists());
+        assert!(pending.exists());
+        publish(&pending, &final_path, &CancellationToken::new()).unwrap();
+        assert!(!pending.exists());
+        assert_eq!(std::fs::read(final_path.join("Channel.class")).unwrap(), b"complete");
+    }
+
+    #[test]
+    fn never_runs_another_build_system_with_maven_output_properties() {
+        let directory = tempfile::tempdir().unwrap();
+        std::fs::write(directory.path().join("Cargo.toml"), "").unwrap();
+        let error = build(
+            directory.path(),
+            &BuildModel::default(),
+            Path::new("unused.jar"),
+            &directory.path().join("private"),
+            &CancellationToken::new(),
+        )
+        .err()
+        .unwrap();
+        assert_eq!(error.message, "Kotlin bridge requires a Maven build root");
+    }
+
+    #[test]
+    fn does_not_find_deleted_sources_in_build_outputs() {
+        let dir = tempfile::tempdir().unwrap();
+        std::fs::create_dir_all(dir.path().join("target/generated")).unwrap();
+        std::fs::write(dir.path().join("target/generated/Old.kt"), "").unwrap();
+        assert!(!has_kotlin(dir.path()));
+        std::fs::write(dir.path().join("New.kt"), "").unwrap();
+        assert!(has_kotlin(dir.path()));
+    }
+
+    #[test]
+    fn parses_sourcefile_and_rejects_truncated_classes() {
+        let mut class = vec![0xca, 0xfe, 0xba, 0xbe, 0, 0, 0, 52, 0, 3, 1, 0, 10];
+        class.extend_from_slice(b"SourceFile");
+        class.extend_from_slice(&[1, 0, 10]);
+        class.extend_from_slice(b"Channel.kt");
+        class.extend_from_slice(&[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 2, 0, 2]);
+        assert_eq!(kotlin_class(&class), Some(true));
+        for end in 0..class.len() {
+            assert!(kotlin_class(&class[..end]).is_none());
+        }
+        let offset = 26;
+        class[offset..offset + 10].copy_from_slice(b"Other.java");
+        assert_eq!(kotlin_class(&class), Some(false));
+    }
+}
diff --git a/crates/ide-build/src/lib.rs b/crates/ide-build/src/lib.rs
index 10dcd9b1c..96358419f 100644
--- a/crates/ide-build/src/lib.rs
+++ b/crates/ide-build/src/lib.rs
@@ -8,6 +8,7 @@
 pub mod application_update;
 pub mod compile;
 pub mod gradle;
+pub mod kotlin_bridge;
 pub mod maven;
 pub mod pom_edit;
 mod process;
diff --git a/crates/ide-build/src/maven.rs b/crates/ide-build/src/maven.rs
index 2c0e3f8fb..7f2561003 100644
--- a/crates/ide-build/src/maven.rs
+++ b/crates/ide-build/src/maven.rs
@@ -601,6 +601,72 @@ impl Resolver {
     }
 }
 
+/// Files and source/resource trees consumed by a launch build. Unresolved custom
+/// roots disable reuse rather than silently omitting an input.
+pub(crate) fn launch_inputs(
+    root: &Path,
+    projects: &[&MavenProject],
+    local_repo: Option<PathBuf>,
+) -> Option<Vec<PathBuf>> {
+    fn roots(el: &Element, parent: &str, dir: &Path, out: &mut Vec<PathBuf>) -> Option<()> {
+        let input =
+            matches!(el.name.as_str(), "sourceDirectory" | "testSourceDirectory" | "sourceDir" | "testSourceDir")
+                || (matches!(parent, "sources" | "sourceDirs" | "testSources" | "testSourceDirs")
+                    && matches!(el.name.as_str(), "source" | "sourceDir" | "testSourceDir"))
+                || (matches!(parent, "resource" | "testResource" | "source" | "testSource") && el.name == "directory")
+                || (parent == "filters" && el.name == "filter");
+        // Profile activation may depend on the presence of an otherwise unrelated file.
+        let activation = parent == "file" && matches!(el.name.as_str(), "exists" | "missing");
+        if input || activation {
+            // Other properties can be overridden by -D, profiles or settings.
+            // Without Maven's effective roots, conservatively disable reuse for them.
+            let value = el
+                .text
+                .trim()
+                .replace("${project.basedir}", &dir.to_string_lossy())
+                .replace("${basedir}", &dir.to_string_lossy());
+            if value.contains("${") {
+                return None;
+            }
+            if !value.is_empty() {
+                out.push(dir.join(value));
+            }
+        }
+        for child in &el.children {
+            roots(child, &el.name, dir, out)?;
+        }
+        Some(())
+    }
+    let mut resolver = Resolver::new(local_repo.or_else(default_local_repo));
+    let mut out = Vec::new();
+    for project in projects {
+        let dir = root.join(&project.dir);
+        // Include all conventional language/resource roots, including nonstandard files under src.
+        out.push(dir.join("src"));
+        let pom = root.join(&project.pom);
+        resolver.context(&pom, 0);
+        let mut path = pom;
+        let mut seen = HashSet::new();
+        loop {
+            let canonical = dunce::canonicalize(&path).ok()?;
+            if !seen.insert(canonical) || seen.len() > MAX_PARENT_DEPTH {
+                return None;
+            }
+            out.push(path.clone());
+            let text = std::fs::read_to_string(&path).ok()?;
+            roots(&xml::parse(&text)?, "", &dir, &mut out)?;
+            let raw = resolver.pom(&path)?;
+            let Some(parent) = raw.parent else { break };
+            path = resolver.parent_path(path.parent()?, &parent)?;
+        }
+    }
+    // Also track imported BOMs read while resolving inheritance.
+    out.extend(resolver.poms.into_keys());
+    out.sort();
+    out.dedup();
+    Some(out)
+}
+
 // ---------------------------------------------------------------- plugins
 
 /// `maven-clean-plugin` → `clean`, `spring-boot-maven-plugin` → `spring-boot`.
diff --git a/crates/ide-build/src/process.rs b/crates/ide-build/src/process.rs
index b598eb791..8177089f0 100644
--- a/crates/ide-build/src/process.rs
+++ b/crates/ide-build/src/process.rs
@@ -37,7 +37,7 @@ fn kill_tree(child: &mut Child) {
 /// `program` as spawnable: a bare name (`mvn`, `mvn.cmd`) resolves on the IDE's
 /// search path — the login shell's `PATH` plus version-manager shims — since the
 /// app's own `PATH` can be minimal and `Command` would not see `mvn` there.
-fn program_path(program: &str, env: &BTreeMap<String, String>) -> std::path::PathBuf {
+pub(crate) fn program_path(program: &str, env: &BTreeMap<String, String>) -> std::path::PathBuf {
     let path = std::path::Path::new(program);
     if !path.is_relative() || path.components().count() > 1 {
         return path.to_path_buf();
diff --git a/crates/ide-core/src/error.rs b/crates/ide-core/src/error.rs
index 7df81c9a5..f78cf37f7 100644
--- a/crates/ide-core/src/error.rs
+++ b/crates/ide-core/src/error.rs
@@ -12,6 +12,15 @@ pub type IdeResult<T> = Result<T, IdeError>;
 pub struct IdeError {
     pub kind: ErrorKind,
     pub message: String,
+    /// Structured detail for errors the UI acts on; `null` for plain errors.
+    #[specta(optional)]
+    pub data: Option<ErrorData>,
+}
+
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize, Type)]
+#[serde(tag = "type", rename_all = "camelCase")]
+pub enum ErrorData {
+    Tool { tool: String, missing: bool },
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize, Type)]
@@ -24,6 +33,7 @@ pub enum ErrorKind {
     /// Document version mismatch; the UI must resync the full text.
     OutOfSync,
     Cancelled,
+    TimedOut,
     /// A required external tool (language server, git, debugger) is unavailable.
     Unavailable,
     Io,
@@ -33,7 +43,21 @@ pub enum ErrorKind {
 
 impl IdeError {
     pub fn new(kind: ErrorKind, message: impl Into<String>) -> Self {
-        Self { kind, message: message.into() }
+        Self { kind, message: message.into(), data: None }
+    }
+    pub fn with_tool(mut self, tool: impl Into<String>) -> Self {
+        if self.data.is_none() {
+            self.data = Some(ErrorData::Tool { tool: tool.into(), missing: false });
+        }
+        self
+    }
+    pub fn missing_tool(tool: impl Into<String>) -> Self {
+        let tool = tool.into();
+        Self {
+            kind: ErrorKind::NotFound,
+            message: format!("{tool} is not installed"),
+            data: Some(ErrorData::Tool { tool, missing: true }),
+        }
     }
     pub fn not_found(m: impl Into<String>) -> Self {
         Self::new(ErrorKind::NotFound, m)
@@ -65,3 +89,30 @@ impl From<std::io::Error> for IdeError {
         Self::new(kind, e.to_string())
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn tool_errors_round_trip_without_changing_diagnostics() {
+        let message = "[error] file.css: Unexpected token\n  1 | }\n";
+        let error = IdeError::invalid(message).with_tool("prettier");
+        let decoded: IdeError = serde_json::from_str(&serde_json::to_string(&error).unwrap()).unwrap();
+        assert_eq!(decoded.message, message);
+        assert_eq!(decoded.data, Some(ErrorData::Tool { tool: "prettier".into(), missing: false }));
+        let missing = IdeError::missing_tool("prettier").with_tool("prettier");
+        assert_eq!(missing.kind, ErrorKind::NotFound);
+        assert_eq!(missing.data, Some(ErrorData::Tool { tool: "prettier".into(), missing: true }));
+    }
+
+    #[test]
+    fn legacy_errors_need_no_data() {
+        let error: IdeError = serde_json::from_str(r#"{"kind":"unavailable","message":"no server"}"#).unwrap();
+        assert!(error.data.is_none());
+        assert_eq!(
+            serde_json::to_value(error).unwrap(),
+            serde_json::json!({"kind":"unavailable","message":"no server","data":null})
+        );
+    }
+}
diff --git a/crates/ide-core/src/settings.rs b/crates/ide-core/src/settings.rs
index 5900f7e80..7f360b1f1 100644
--- a/crates/ide-core/src/settings.rs
+++ b/crates/ide-core/src/settings.rs
@@ -276,6 +276,8 @@ pub struct AppearanceSettings {
     /// Apply `ui_font_family` / `ui_font_size` (otherwise the theme's).
     pub use_custom_font: bool,
     pub ui_font_family: String,
+    /// Font tried when `ui_font_family` lacks a glyph; empty = none.
+    pub ui_font_fallback: String,
     pub contrast_scrollbars: bool,
     /// Adjust colours for red-green vision deficiency.
     pub red_green_vision: bool,
@@ -292,6 +294,7 @@ pub struct AppearanceSettings {
     pub editor_antialiasing: String,
     pub show_tool_window_bars: bool,
     pub show_tool_window_names: bool,
+    pub show_tool_window_badges: bool,
     pub widescreen_tool_windows: bool,
     /// Status bar widgets shown (`true`) or hidden (`false`) by the user
     /// (status bar context menu); widgets not listed use their default.
@@ -325,6 +328,7 @@ impl Default for AppearanceSettings {
             zoom: 100,
             use_custom_font: false,
             ui_font_family: "Inter".into(),
+            ui_font_fallback: String::new(),
             contrast_scrollbars: false,
             red_green_vision: false,
             different_tool_window_background: false,
@@ -338,6 +342,7 @@ impl Default for AppearanceSettings {
             editor_antialiasing: "greyscale".into(),
             show_tool_window_bars: true,
             show_tool_window_names: false,
+            show_tool_window_badges: true,
             widescreen_tool_windows: false,
             status_bar_widgets: BTreeMap::new(),
             main_toolbar: None,
@@ -503,9 +508,50 @@ pub struct LanguagesSettings {
     pub rust: RustSettings,
     pub go: GoSettings,
     pub typescript: TypeScriptSettings,
+    pub prettier: PrettierSettings,
     pub java: JavaSettings,
 }
 
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize, Type)]
+#[serde(default, rename_all = "camelCase")]
+pub struct PrettierSettings {
+    /// Empty path: project node_modules, managed installation, then PATH.
+    pub path: String,
+    pub languages: Vec<String>,
+    /// Prefer Prettier even when a language server offers formatting.
+    pub prefer: bool,
+    pub run_on_save: bool,
+}
+
+impl Default for PrettierSettings {
+    fn default() -> Self {
+        Self {
+            path: String::new(),
+            languages: [
+                "markdown",
+                "yaml",
+                "css",
+                "scss",
+                "less",
+                "html",
+                "graphql",
+                "javascript",
+                "javascriptreact",
+                "typescript",
+                "typescriptreact",
+                "json",
+                "jsonc",
+                "vue",
+            ]
+            .into_iter()
+            .map(String::from)
+            .collect(),
+            prefer: false,
+            run_on_save: false,
+        }
+    }
+}
+
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize, Type)]
 #[serde(default, rename_all = "camelCase")]
 pub struct PythonSettings {
@@ -719,6 +765,35 @@ impl Settings {
 mod tests {
     use super::*;
 
+    #[test]
+    fn ui_font_fallback_defaults_empty_and_round_trips() {
+        let old: Settings = serde_json::from_str(r#"{"appearance":{"useCustomFont":true}}"#).unwrap();
+        assert!(old.appearance.ui_font_fallback.is_empty());
+        for family in ["", "Songti SC", "Maple Mono NF CN"] {
+            let mut settings = Settings::default();
+            settings.appearance.ui_font_fallback = family.into();
+            let json = serde_json::to_value(&settings).unwrap();
+            assert_eq!(json["appearance"]["uiFontFallback"], family);
+            let restored: Settings = serde_json::from_value(json).unwrap();
+            assert_eq!(restored.appearance.ui_font_fallback, family);
+        }
+    }
+
+    #[test]
+    fn tool_window_badges_default_on_and_round_trip() {
+        let old: Settings = serde_json::from_str(r#"{"appearance":{"showToolWindowNames":true}}"#).unwrap();
+        assert!(old.appearance.show_tool_window_badges);
+        assert!(Settings::default().appearance.show_tool_window_badges);
+        for enabled in [false, true] {
+            let mut settings = Settings::default();
+            settings.appearance.show_tool_window_badges = enabled;
+            let json = serde_json::to_value(&settings).unwrap();
+            assert_eq!(json["appearance"]["showToolWindowBadges"], enabled);
+            let restored: Settings = serde_json::from_value(json).unwrap();
+            assert_eq!(restored.appearance.show_tool_window_badges, enabled);
+        }
+    }
+
     #[test]
     fn main_menu_style_defaults_and_round_trips() {
         let old: Settings = serde_json::from_str(r#"{"appearance":{"compactMode":true}}"#).unwrap();
diff --git a/crates/ide-dap/src/tests.rs b/crates/ide-dap/src/tests.rs
index 6bcd57b65..e1fb0ecae 100644
--- a/crates/ide-dap/src/tests.rs
+++ b/crates/ide-dap/src/tests.rs
@@ -905,6 +905,7 @@ fn godot_registry(port: u16, command: &str, args: &[&str]) -> Arc<LanguageRegist
         indent: None,
         ui_mode: None,
         framework_ui_modes: Vec::new(),
+        formatter: None,
         tree_sitter: None,
         language_servers: vec![],
         debugger: Some(ide_language::DebuggerConfig {
diff --git a/crates/ide-fonts/Cargo.toml b/crates/ide-fonts/Cargo.toml
index 5c6695271..52b849b84 100644
--- a/crates/ide-fonts/Cargo.toml
+++ b/crates/ide-fonts/Cargo.toml
@@ -7,10 +7,11 @@ license.workspace = true
 
 [dependencies]
 serde.workspace = true
+serde_json.workspace = true
 specta.workspace = true
 
 [target.'cfg(target_os = "macos")'.dependencies]
-objc2-core-foundation = { version = "0.3", default-features = false, features = ["std", "CFArray", "CFDictionary", "CFNumber", "CFString"] }
+objc2-core-foundation = { version = "0.3", default-features = false, features = ["std", "CFArray", "CFDictionary", "CFNumber", "CFString", "CFURL"] }
 objc2-core-text = { version = "0.3", default-features = false, features = ["std", "CTFontCollection", "CTFontDescriptor", "CTFontTraits"] }
 
 [target.'cfg(windows)'.dependencies]
diff --git a/crates/ide-fonts/src/lib.rs b/crates/ide-fonts/src/lib.rs
index 7274544e5..341febdea 100644
--- a/crates/ide-fonts/src/lib.rs
+++ b/crates/ide-fonts/src/lib.rs
@@ -1,8 +1,7 @@
 //! The font families installed on this machine, for the font pickers in
 //! Settings (editor, typography fallback, terminal, UI font).
 //!
-//! Each platform asks the font system the WebView itself resolves CSS
-//! `font-family` names against, so every listed name renders: CoreText on
+//! Each platform asks the native font system for installed families: CoreText on
 //! macOS, DirectWrite on Windows, fontconfig (`fc-list`) on Linux and the BSDs.
 //! The list is read on first use and cached until explicitly refreshed; the
 //! query can take a few hundred milliseconds, so callers run it off the UI and
@@ -84,14 +83,164 @@ pub fn parse_fc_list(output: &str) -> Vec<(String, bool)> {
         .collect()
 }
 
+/// Binary font bundle: little-endian u32 JSON-header length, a face metadata
+/// array, then raw font bytes. Paths never cross IPC; only CoreText-enumerated
+/// files under user font directories can be read, selected by family name.
+/// Includes only the nearest regular/bold faces and their optional italics.
+pub fn user_font_data(family: &str) -> std::io::Result<Vec<u8>> {
+    #[cfg(target_os = "macos")]
+    {
+        let entries = imp::user_faces();
+        bundle_family(family, &entries)
+    }
+    #[cfg(not(target_os = "macos"))]
+    {
+        let _ = family;
+        Err(std::io::Error::new(std::io::ErrorKind::Unsupported, "User font loading is macOS only"))
+    }
+}
+
+#[cfg(any(target_os = "macos", test))]
+#[derive(Debug)]
+struct UserFace {
+    family: String,
+    path: std::path::PathBuf,
+    weight: u16,
+    italic: bool,
+}
+
+#[cfg(any(target_os = "macos", test))]
+fn user_font_path(path: &std::path::Path, roots: &[std::path::PathBuf]) -> Option<std::path::PathBuf> {
+    let path = path.canonicalize().ok()?;
+    roots.iter().any(|root| path.starts_with(root)).then_some(path)
+}
+
+#[cfg(any(target_os = "macos", test))]
+fn family_faces<'a>(family: &str, entries: &'a [UserFace]) -> Vec<&'a UserFace> {
+    let mut selected: Vec<&UserFace> = Vec::new();
+    for italic in [false, true] {
+        for weight in [400u16, 700] {
+            let closest = entries
+                .iter()
+                .filter(|e| e.family.eq_ignore_ascii_case(family.trim()) && e.italic == italic)
+                .min_by_key(|e| (e.weight.abs_diff(weight), e.weight, &e.path));
+            if let Some(face) = closest
+                && !selected.iter().any(|f| std::ptr::eq(*f, face))
+            {
+                selected.push(face);
+            }
+        }
+    }
+    selected
+}
+
+#[cfg(any(target_os = "macos", test))]
+fn bundle_family(family: &str, entries: &[UserFace]) -> std::io::Result<Vec<u8>> {
+    #[derive(Serialize)]
+    struct Face {
+        weight: u16,
+        style: &'static str,
+        offset: usize,
+        length: usize,
+    }
+    let mut faces = Vec::new();
+    let mut data = Vec::new();
+    let mut files = BTreeMap::new();
+    // Bound large CJK families to regular/bold and their nearest italic faces.
+    for entry in family_faces(family, entries) {
+        // Reject a file replaced by a symlink after enumeration.
+        if entry.path.canonicalize()? != entry.path {
+            return Err(std::io::Error::new(std::io::ErrorKind::PermissionDenied, "Font file changed"));
+        }
+        let (offset, length) = if let Some(range) = files.get(&entry.path) {
+            *range
+        } else {
+            let bytes = std::fs::read(&entry.path)?;
+            let range = (data.len(), bytes.len());
+            data.extend(bytes);
+            files.insert(entry.path.clone(), range);
+            range
+        };
+        faces.push(Face {
+            weight: entry.weight,
+            style: if entry.italic { "italic" } else { "normal" },
+            offset,
+            length,
+        });
+    }
+    if faces.is_empty() {
+        return Err(std::io::Error::new(std::io::ErrorKind::NotFound, "No installed user font family"));
+    }
+    let header = serde_json::to_vec(&faces)?;
+    let mut out = (header.len() as u32).to_le_bytes().to_vec();
+    out.extend(header);
+    out.extend(data);
+    Ok(out)
+}
+
 #[cfg(target_os = "macos")]
 mod imp {
-    use objc2_core_foundation::{CFArray, CFDictionary, CFNumber, CFString, CFType};
+    use objc2_core_foundation::{CFArray, CFDictionary, CFNumber, CFString, CFType, CFURL};
     use objc2_core_text::{
         CTFontCollection, CTFontDescriptor, CTFontSymbolicTraits, kCTFontFamilyNameAttribute, kCTFontSymbolicTrait,
-        kCTFontTraitsAttribute,
+        kCTFontTraitsAttribute, kCTFontURLAttribute, kCTFontWeightTrait,
     };
 
+    pub(crate) fn user_faces() -> Vec<super::UserFace> {
+        let mut roots = vec![std::path::PathBuf::from("/Library/Fonts")];
+        if let Some(home) = std::env::var_os("HOME") {
+            roots.push(std::path::PathBuf::from(home).join("Library/Fonts"));
+        }
+        let roots: Vec<_> = roots.into_iter().filter_map(|r| r.canonicalize().ok()).collect();
+        // SAFETY: CoreText descriptors carry documented CFString, CFURL and trait dictionary values.
+        unsafe {
+            let collection = CTFontCollection::from_available_fonts(None);
+            let Some(descriptors) = collection.matching_font_descriptors() else { return Vec::new() };
+            let mut seen = std::collections::BTreeSet::new();
+            descriptors
+                .cast_unchecked::<CTFontDescriptor>()
+                .iter()
+                .filter_map(|d| {
+                    let family = d.attribute(kCTFontFamilyNameAttribute)?.downcast::<CFString>().ok()?.to_string();
+                    let path = d.attribute(kCTFontURLAttribute)?.downcast::<CFURL>().ok()?.to_file_path()?;
+                    let path = super::user_font_path(&path, &roots)?;
+                    let traits = d.attribute(kCTFontTraitsAttribute)?.downcast::<CFDictionary>().ok()?;
+                    let traits = traits.cast_unchecked::<CFString, CFType>();
+                    let symbolic = traits
+                        .get(kCTFontSymbolicTrait)
+                        .and_then(|n| n.downcast::<CFNumber>().ok())
+                        .and_then(|n| n.as_i64())
+                        .unwrap_or(0) as u32;
+                    let weight = traits
+                        .get(kCTFontWeightTrait)
+                        .and_then(|n| n.downcast::<CFNumber>().ok())
+                        .and_then(|n| n.as_f64())
+                        .unwrap_or(0.0);
+                    // CoreText's normalized weight values corresponding to CSS's nine standard weights.
+                    let weight = [
+                        (-0.8, 100),
+                        (-0.6, 200),
+                        (-0.4, 300),
+                        (0.0, 400),
+                        (0.23, 500),
+                        (0.3, 600),
+                        (0.4, 700),
+                        (0.56, 800),
+                        (0.62, 900),
+                    ]
+                    .into_iter()
+                    .min_by(|(a, _), (b, _)| (weight - a).abs().total_cmp(&(weight - b).abs()))?
+                    .1;
+                    let italic = symbolic & CTFontSymbolicTraits::TraitItalic.0 != 0;
+                    if !seen.insert((family.clone(), path.clone(), weight, italic)) {
+                        return None;
+                    }
+                    Some(super::UserFace { family, path, weight, italic })
+                })
+                .collect()
+        }
+    }
+
     /// Every face CoreText makes available to this process, as (family, fixed pitch).
     pub(crate) fn list(_refresh: bool) -> Vec<(String, bool)> {
         // SAFETY: CoreText's documented types: the matching descriptors array
@@ -210,6 +359,92 @@ mod tests {
     use super::*;
     use std::sync::atomic::{AtomicUsize, Ordering};
 
+    #[test]
+    fn selects_only_regular_bold_and_matching_italics_from_dense_families() {
+        let entries: Vec<_> = [false, true]
+            .into_iter()
+            .flat_map(|italic| {
+                (100..=900).step_by(100).map(move |weight| UserFace {
+                    family: "CJK".into(),
+                    path: format!("{weight}-{italic}.ttf").into(),
+                    weight,
+                    italic,
+                })
+            })
+            .collect();
+        let selected = family_faces(" cjk ", &entries);
+        assert_eq!(
+            selected.iter().map(|f| (f.weight, f.italic)).collect::<Vec<_>>(),
+            [(400, false), (700, false), (400, true), (700, true),]
+        );
+        assert!(family_faces("unknown", &entries).is_empty());
+    }
+
+    #[test]
+    fn selects_nearest_available_weights_once_with_optional_italics() {
+        let entries: Vec<_> = [(300, false), (500, false), (800, false), (500, true)]
+            .into_iter()
+            .map(|(weight, italic)| UserFace {
+                family: "Sparse".into(),
+                path: format!("{weight}-{italic}.ttf").into(),
+                weight,
+                italic,
+            })
+            .collect();
+        let selected = family_faces("Sparse", &entries);
+        assert_eq!(
+            selected.iter().map(|f| (f.weight, f.italic)).collect::<Vec<_>>(),
+            [(300, false), (800, false), (500, true),]
+        );
+        assert_eq!(family_faces("Sparse", &entries[..1]).len(), 1);
+    }
+
+    #[test]
+    fn bundle_only_reads_enumerated_family_faces() {
+        let root = std::env::current_dir().unwrap().join(format!("../../.font-bundle-test-{}", std::process::id()));
+        std::fs::create_dir_all(&root).unwrap();
+        let root = root.canonicalize().unwrap();
+        let regular = root.join("regular.ttf");
+        let bold = root.join("bold.ttf");
+        std::fs::write(&regular, [1, 2, 3]).unwrap();
+        std::fs::write(&bold, [4, 5]).unwrap();
+        let entries = [
+            UserFace { family: "Test Nerd Font".into(), path: regular.clone(), weight: 400, italic: false },
+            UserFace { family: "Test Nerd Font".into(), path: bold, weight: 700, italic: false },
+            // A non-selected face is never opened, even if its file has disappeared.
+            UserFace { family: "Test Nerd Font".into(), path: root.join("thin.ttf"), weight: 100, italic: false },
+        ];
+        let result = bundle_family("test nerd font", &entries).unwrap();
+        let len = u32::from_le_bytes(result[..4].try_into().unwrap()) as usize;
+        let faces: serde_json::Value = serde_json::from_slice(&result[4..4 + len]).unwrap();
+        assert_eq!(faces[0]["weight"], 400);
+        assert_eq!(faces[1]["weight"], 700);
+        assert_eq!(faces.as_array().unwrap().len(), 2);
+        assert_eq!(&result[4 + len..], &[1, 2, 3, 4, 5]);
+        // Existing files are not inputs: neither paths nor unenumerated families grant access.
+        assert!(bundle_family(regular.to_str().unwrap(), &entries).is_err());
+        assert!(bundle_family("Unenumerated", &entries).is_err());
+        assert!(user_font_path(&regular, &[]).is_none());
+        assert!(user_font_path(&regular, std::slice::from_ref(&root)).is_some());
+        // Multiple selected descriptors in a collection still transfer the file only once.
+        let shared = [
+            UserFace { family: "Collection".into(), path: regular.clone(), weight: 400, italic: false },
+            UserFace { family: "Collection".into(), path: regular, weight: 700, italic: false },
+        ];
+        let result = bundle_family("Collection", &shared).unwrap();
+        let len = u32::from_le_bytes(result[..4].try_into().unwrap()) as usize;
+        let faces: serde_json::Value = serde_json::from_slice(&result[4..4 + len]).unwrap();
+        assert_eq!(faces[0]["offset"], faces[1]["offset"]);
+        assert_eq!(&result[4 + len..], &[1, 2, 3]);
+        #[cfg(unix)]
+        {
+            let link = root.join("outside.ttf");
+            std::os::unix::fs::symlink(std::env::current_exe().unwrap(), &link).unwrap();
+            assert!(user_font_path(&link, std::slice::from_ref(&root)).is_none());
+        }
+        std::fs::remove_dir_all(root).unwrap();
+    }
+
     fn fam(name: &str, monospaced: bool) -> FontFamily {
         FontFamily { name: name.into(), monospaced }
     }
diff --git a/crates/ide-host/Cargo.toml b/crates/ide-host/Cargo.toml
index 4518fa0ff..c63304344 100644
--- a/crates/ide-host/Cargo.toml
+++ b/crates/ide-host/Cargo.toml
@@ -48,7 +48,7 @@ parking_lot.workspace = true
 dunce.workspace = true
 dirs.workspace = true
 uuid.workspace = true
+tempfile.workspace = true
 
 [dev-dependencies]
 tokio = { workspace = true, features = ["rt-multi-thread", "macros", "io-util", "test-util"] }
-tempfile.workspace = true
diff --git a/crates/ide-host/src/formatter.rs b/crates/ide-host/src/formatter.rs
new file mode 100644
index 000000000..2da08e368
--- /dev/null
+++ b/crates/ide-host/src/formatter.rs
@@ -0,0 +1,107 @@
+//! Select the document's formatting provider before executing it on this host.
+
+use crate::Host;
+use ide_core::event::NotifyLevel;
+use ide_core::settings::PrettierSettings;
+use ide_core::{DocId, IdeError, IdeEvent, IdeResult, Range, TextEdit};
+use ide_language::FormatterConfig;
+use ide_lsp::types::FormatOptions;
+use ide_tools::{Tools, formatter};
+
+fn external_selected(config: Option<&FormatterConfig>, language: &str, settings: &PrettierSettings, lsp: bool) -> bool {
+    config.is_some_and(|c| c.tool == "prettier")
+        && settings.languages.iter().any(|l| l == language)
+        && (settings.prefer || !lsp)
+}
+
+pub async fn format(
+    host: &Host,
+    window: &str,
+    doc: DocId,
+    range: Option<Range>,
+    options: FormatOptions,
+) -> IdeResult<Vec<TextEdit>> {
+    let project = host.project(window)?;
+    let snap = project.documents.snapshot(doc)?;
+    let settings = project.settings.effective();
+    let prettier = &settings.languages.prettier;
+    let language = project.languages.get(&snap.language);
+    let config = language.as_ref().and_then(|l| l.formatter.as_ref());
+    let candidate =
+        config.is_some_and(|c| c.tool == "prettier") && prettier.languages.iter().any(|l| l == snap.language.as_str());
+    let lsp = if candidate && !prettier.prefer { project.lsp.can_format(doc).await? } else { false };
+    if !external_selected(config, snap.language.as_str(), prettier, lsp) {
+        if options.on_save && !settings.editor.format_on_save {
+            return Ok(Vec::new());
+        }
+        return project.lsp.format(doc, range, options).await;
+    }
+    if options.on_save && !prettier.run_on_save {
+        return Ok(Vec::new());
+    }
+    host.require_trust(window)?;
+    if snap.read_only {
+        return Err(IdeError::invalid("The file is read-only"));
+    }
+    let config = config.unwrap().clone();
+    let custom = ide_sdk::apply::setting_path(&project.root, &prettier.path);
+    let tools = Tools::new(&host.data_dir);
+    let whole_selection = range.is_some() && !config.range;
+    let edits: IdeResult<Vec<TextEdit>> = tokio::task::spawn_blocking(move || {
+        let text = ide_text::Document::new(&snap.text);
+        let offsets = range.map(|r| (text.pos_to_offset(r.start), text.pos_to_offset(r.end)));
+        let mut command = tools.formatter_command(&config.tool, &snap.path, custom.as_deref())?;
+        command.current_dir(snap.path.parent().ok_or_else(|| IdeError::invalid("Prettier: file has no directory"))?);
+        command.args(formatter::arguments(&config, &snap.path, options.tab_size, options.insert_spaces, offsets));
+        let formatted = formatter::run(command, &snap.text, &Default::default())?;
+        Ok(text
+            .diff(&formatted)
+            .changes
+            .into_iter()
+            .map(|c| TextEdit {
+                range: Range::new(text.offset_to_pos(c.from), text.offset_to_pos(c.to)),
+                new_text: c.insert,
+            })
+            .collect())
+    })
+    .await
+    .map_err(|e| IdeError::internal(e.to_string()))?;
+    if edits.is_ok() && whole_selection {
+        project.sink.emit(IdeEvent::Notify {
+            level: NotifyLevel::Info,
+            title: "Prettier".into(),
+            body: Some(
+                "Prettier does not support selection formatting for this language; formatted the whole file".into(),
+            ),
+        });
+    }
+    edits.map_err(|e| e.with_tool("prettier"))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn language_enablement_and_preference_preserve_lsp_formatters() {
+        let languages = ide_language::LanguageRegistry::load(None).unwrap();
+        let mut settings = PrettierSettings::default();
+        for lang in languages.all() {
+            for lsp in [false, true] {
+                let configured = lang.formatter.as_ref().is_some_and(|f| f.tool == "prettier");
+                assert_eq!(
+                    external_selected(lang.formatter.as_ref(), lang.id.as_str(), &settings, lsp),
+                    configured && !lsp,
+                    "{}",
+                    lang.id
+                );
+            }
+        }
+        let ts = languages.get(&ide_core::LanguageId::new("typescript")).unwrap();
+        settings.prefer = true;
+        assert!(external_selected(ts.formatter.as_ref(), "typescript", &settings, true));
+        settings.languages.clear();
+        assert!(!external_selected(ts.formatter.as_ref(), "typescript", &settings, false));
+        assert!(!external_selected(None, "rust", &settings, false));
+    }
+}
diff --git a/crates/ide-host/src/kotlin_bridge.rs b/crates/ide-host/src/kotlin_bridge.rs
new file mode 100644
index 000000000..c29be5a29
--- /dev/null
+++ b/crates/ide-host/src/kotlin_bridge.rs
@@ -0,0 +1,429 @@
+//! Saved Kotlin -> isolated Maven output -> marked JDT libraries.
+
+use ide_build::kotlin_bridge::{self, Outcome, ProjectLibraries};
+use ide_core::event::NotifyLevel;
+use ide_core::{CancellationToken, Diagnostic, IdeEvent, Pos, Range, Severity, SharedSink};
+use ide_lsp::LspManager;
+use ide_workspace::SettingsStore;
+use ide_workspace::documents::DocumentObserver;
+use parking_lot::Mutex;
+use serde::{Deserialize, Serialize};
+use std::collections::BTreeSet;
+use std::path::{Path, PathBuf};
+use std::sync::{
+    Arc,
+    atomic::{AtomicBool, Ordering},
+};
+use std::time::Duration;
+use tokio::sync::Notify;
+
+const DELAY: Duration = Duration::from_millis(750);
+const SOURCE: &str = "kotlin-bridge";
+const COMMAND: &str = "openidea.kotlin.replace";
+
+#[derive(Default)]
+struct Revision {
+    generation: u64,
+    cancel: CancellationToken,
+}
+
+impl Revision {
+    fn change(&mut self) {
+        self.cancel.cancel();
+        self.generation += 1;
+        self.cancel = CancellationToken::new();
+    }
+    fn current(&self, generation: u64) -> bool {
+        self.generation == generation && !self.cancel.is_cancelled()
+    }
+}
+
+#[derive(Clone, Default, Serialize, Deserialize)]
+struct MavenOptions {
+    offline: bool,
+    profiles: Vec<String>,
+}
+
+pub(crate) struct KotlinBridge {
+    root: PathBuf,
+    cache: PathBuf,
+    bundle: Option<PathBuf>,
+    settings: Arc<SettingsStore>,
+    lsp: Arc<LspManager>,
+    sink: SharedSink,
+    trusted: Arc<AtomicBool>,
+    lifetime: CancellationToken,
+    revision: Mutex<Revision>,
+    changed: Notify,
+    options: Mutex<MavenOptions>,
+    worker: Mutex<Option<tokio::task::JoinHandle<()>>>,
+}
+
+impl KotlinBridge {
+    pub(crate) fn new(
+        root: PathBuf,
+        cache: PathBuf,
+        data: &Path,
+        settings: Arc<SettingsStore>,
+        lsp: Arc<LspManager>,
+        sink: SharedSink,
+        trusted: Arc<AtomicBool>,
+    ) -> Arc<Self> {
+        let options = std::fs::read(cache.join("kotlin-bridge-options.json"))
+            .ok()
+            .and_then(|bytes| serde_json::from_slice(&bytes).ok())
+            .unwrap_or_default();
+        Arc::new(Self {
+            root,
+            cache,
+            bundle: ide_sdk::java::kotlin_bridge_bundle(data),
+            settings,
+            lsp,
+            sink,
+            trusted,
+            lifetime: CancellationToken::new(),
+            revision: Mutex::new(Revision::default()),
+            changed: Notify::new(),
+            options: Mutex::new(options),
+            worker: Mutex::new(None),
+        })
+    }
+
+    pub(crate) fn start(self: &Arc<Self>, runtime: &tokio::runtime::Handle) {
+        let bridge = self.clone();
+        *self.worker.lock() = Some(runtime.spawn(async move { bridge.run().await }));
+        self.schedule();
+    }
+
+    pub(crate) fn configure_maven(&self, offline: bool, profiles: Vec<String>) {
+        let options = MavenOptions { offline, profiles };
+        if let Ok(bytes) = serde_json::to_vec(&options) {
+            let _ = std::fs::create_dir_all(&self.cache);
+            let _ = std::fs::write(self.cache.join("kotlin-bridge-options.json"), bytes);
+        }
+        *self.options.lock() = options;
+        self.schedule();
+    }
+
+    pub(crate) async fn shutdown(&self) {
+        self.stop();
+        let worker = self.worker.lock().take();
+        if let Some(worker) = worker {
+            let _ = worker.await;
+        }
+    }
+
+    pub(crate) fn schedule(&self) {
+        if self.lifetime.is_cancelled() {
+            return;
+        }
+        self.revision.lock().change();
+        self.changed.notify_one();
+    }
+
+    pub(crate) fn files_changed<'a>(&self, mut paths: impl Iterator<Item = &'a PathBuf>) {
+        let settings = self.settings.effective();
+        if paths.any(|path| relevant_change(&self.root, path, &settings)) {
+            self.schedule();
+        }
+    }
+
+    pub(crate) fn stop(&self) {
+        self.lifetime.cancel();
+        self.revision.lock().cancel.cancel();
+    }
+
+    async fn replace(&self, projects: &[ProjectLibraries], cancel: &CancellationToken) -> ide_core::IdeResult<()> {
+        let snapshot = serde_json::to_value(projects).map_err(|e| ide_core::IdeError::internal(e.to_string()))?;
+        let response = self.lsp.jdtls_command_cancellable(&self.root, COMMAND, vec![snapshot], cancel).await?;
+        if response.as_u64().is_none() {
+            return Err(ide_core::IdeError::unavailable(
+                "Kotlin bridge command did not acknowledge its library snapshot",
+            ));
+        }
+        Ok(())
+    }
+
+    async fn run(self: Arc<Self>) {
+        let mut diagnostics = BTreeSet::new();
+        let mut last_failure = String::new();
+        let mut initialized = false;
+        // Also retain directories from unacknowledged replacements: JDT may have applied them.
+        let mut published = Vec::new();
+        loop {
+            tokio::select! {
+                _ = self.lifetime.cancelled() => return,
+                _ = self.changed.notified() => {},
+            }
+            let (generation, cancel) = {
+                let state = self.revision.lock();
+                (state.generation, state.cancel.clone())
+            };
+            if !self.trusted.load(Ordering::Acquire) {
+                continue;
+            }
+            if !debounce(&cancel, &self.lifetime).await {
+                continue;
+            }
+            let root = self.root.clone();
+            let cache = self.cache.clone();
+            let settings = self.settings.effective();
+            let has_sources = tokio::task::spawn_blocking(move || {
+                let model = crate::ops::build::load(&root, &cache, &settings);
+                let enabled =
+                    model.maven.as_ref().is_some_and(|m| !m.projects.is_empty()) && kotlin_bridge::has_kotlin(&root);
+                (model, enabled)
+            })
+            .await;
+            let Ok((mut model, enabled)) = has_sources else { continue };
+            if !self.revision.lock().current(generation) {
+                continue;
+            }
+            if !enabled {
+                if self.cache.join("kotlin-bridge").exists()
+                    && let Err(error) = self.replace(&[], &cancel).await
+                {
+                    if !cancel.is_cancelled() {
+                        tracing::warn!("Kotlin library withdrawal: {error}");
+                    }
+                    continue;
+                }
+                for old in published.drain(..) {
+                    remove_directory(old).await;
+                }
+                self.clear_diagnostics(&mut diagnostics);
+                last_failure.clear();
+                continue;
+            }
+            if let Some(maven) = &mut model.maven {
+                let options = self.options.lock();
+                for module in &mut maven.projects {
+                    if options.offline {
+                        module.options.push("-o".into());
+                    }
+                    if !options.profiles.is_empty() {
+                        module.options.push(format!("-P{}", options.profiles.join(",")));
+                    }
+                }
+            }
+            let Some(bundle) = self.bundle.clone() else {
+                self.failure("Kotlin bridge bundle is unavailable".into(), &mut diagnostics, &mut last_failure);
+                continue;
+            };
+            // Clear entries persisted by an earlier incarnation only before our first build.
+            if !initialized {
+                if let Err(error) = self.replace(&[], &cancel).await {
+                    if !cancel.is_cancelled() {
+                        self.failure(error.message, &mut diagnostics, &mut last_failure);
+                    }
+                    continue;
+                }
+                initialized = true;
+            }
+            let directory = self.cache.join(format!("kotlin-bridge/{}", uuid::Uuid::new_v4()));
+            let staging = directory.clone();
+            let root = self.root.clone();
+            let token = cancel.clone();
+            let result =
+                tokio::task::spawn_blocking(move || kotlin_bridge::build(&root, &model, &bundle, &staging, &token))
+                    .await;
+            if !self.revision.lock().current(generation) || self.lifetime.is_cancelled() {
+                remove_directory(directory).await;
+                continue;
+            }
+            match result {
+                Ok(Ok(Outcome { success: true, projects, .. })) => {
+                    match self.replace(&projects, &cancel).await {
+                        Ok(()) => {
+                            for old in published.drain(..) {
+                                remove_directory(old).await;
+                            }
+                            published.push(directory);
+                            self.clear_diagnostics(&mut diagnostics);
+                            last_failure.clear();
+                        }
+                        Err(error) => {
+                            // Keep both snapshots until an acknowledged replacement.
+                            published.push(directory);
+                            if !cancel.is_cancelled() {
+                                self.failure(error.message, &mut diagnostics, &mut last_failure);
+                            }
+                        }
+                    }
+                }
+                other => {
+                    let text = match other {
+                        Ok(Ok(outcome)) => outcome
+                            .messages
+                            .iter()
+                            .filter(|m| m.severity == Severity::Error)
+                            .map(|m| m.text.as_str())
+                            .collect::<Vec<_>>()
+                            .join("\n"),
+                        Ok(Err(error)) => error.message,
+                        Err(error) => error.to_string(),
+                    };
+                    self.failure(text, &mut diagnostics, &mut last_failure);
+                    remove_directory(directory).await;
+                }
+            }
+        }
+    }
+
+    fn clear_diagnostics(&self, paths: &mut BTreeSet<PathBuf>) {
+        for path in std::mem::take(paths) {
+            self.sink.emit(IdeEvent::Diagnostics { path: path.into(), source: SOURCE.into(), items: Vec::new() });
+        }
+    }
+
+    fn failure(&self, text: String, paths: &mut BTreeSet<PathBuf>, previous: &mut String) {
+        let text = if text.is_empty() { "Kotlin compilation failed".to_owned() } else { text };
+        let text = format!("{text}\nJava temporarily uses the last successfully compiled Kotlin API.");
+        self.clear_diagnostics(paths);
+        let path = self.root.join("pom.xml");
+        paths.insert(path.clone());
+        self.sink.emit(IdeEvent::Diagnostics {
+            path: path.into(),
+            source: SOURCE.into(),
+            items: vec![Diagnostic {
+                range: Range { start: Pos { line: 0, col: 0 }, end: Pos { line: 0, col: 0 } },
+                severity: Severity::Error,
+                message: text.clone(),
+                source: Some(SOURCE.into()),
+                server: Some(SOURCE.into()),
+                code: None,
+                unnecessary: false,
+                deprecated: false,
+            }],
+        });
+        if previous != &text {
+            self.sink.emit(IdeEvent::Notify {
+                level: NotifyLevel::Error,
+                title: "Kotlin editor compilation failed".into(),
+                body: Some(text.clone()),
+            });
+            *previous = text;
+        }
+    }
+}
+
+fn relevant_change(root: &Path, path: &Path, settings: &ide_core::settings::Settings) -> bool {
+    let input = path.extension().is_some_and(|e| e == "kt")
+        || path.file_name().is_some_and(|n| n == "pom.xml" || n == "mvnw" || n == "mvnw.cmd")
+        || path.components().any(|c| c.as_os_str() == ".mvn");
+    let Ok(relative) = path.strip_prefix(root) else {
+        // Content roots outside the project only contribute Kotlin sources.
+        return path.extension().is_some_and(|e| e == "kt");
+    };
+    // Build outputs and generated sources (e.g. KSP's `.kt` under target/) never trigger,
+    // so a build cannot schedule itself.
+    if relative.components().any(|c| {
+        matches!(
+            c.as_os_str().to_str(),
+            Some("target" | "build" | "out" | "bin" | ".git" | "node_modules" | ".openidea")
+        )
+    }) || ide_vfs::ExcludeMatcher::new(&settings.exclude_globs()).is_excluded(relative)
+    {
+        return false;
+    }
+    if input {
+        return true;
+    }
+    if path.extension().is_some() {
+        return false;
+    }
+    // Works for deleted directories too; the module POM remains on disk.
+    path.ancestors().take_while(|ancestor| ancestor.starts_with(root)).any(|ancestor| {
+        ancestor.file_name().is_some_and(|name| name == "src")
+            && ancestor.parent().is_some_and(|module| module.join("pom.xml").is_file())
+    })
+}
+
+async fn debounce(cancel: &CancellationToken, lifetime: &CancellationToken) -> bool {
+    tokio::select! {
+        _ = lifetime.cancelled() => false,
+        _ = cancel.cancelled() => false,
+        _ = tokio::time::sleep(DELAY) => true,
+    }
+}
+
+async fn remove_directory(path: PathBuf) {
+    let _ = tokio::task::spawn_blocking(move || std::fs::remove_dir_all(path)).await;
+}
+
+impl DocumentObserver for KotlinBridge {
+    fn saved(&self, _doc: ide_core::DocId, path: &Path, _text: &str) {
+        self.files_changed(std::iter::once(&path.to_path_buf()));
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn target_package_directory_does_not_trigger() {
+        let dir = tempfile::tempdir().unwrap();
+        std::fs::write(dir.path().join("pom.xml"), "").unwrap();
+        assert!(!relevant_change(dir.path(), &dir.path().join("target/classes/probe"), &Default::default()));
+        let generated = dir.path().join("target/generated-sources/ksp/main/kotlin/Gen.kt");
+        assert!(!relevant_change(dir.path(), &generated, &Default::default()));
+        assert!(relevant_change(dir.path(), &dir.path().join("src/main/kotlin/A.kt"), &Default::default()));
+    }
+
+    #[test]
+    fn deleted_source_package_triggers_unless_excluded() {
+        let dir = tempfile::tempdir().unwrap();
+        std::fs::create_dir_all(dir.path().join("module")).unwrap();
+        std::fs::write(dir.path().join("module/pom.xml"), "").unwrap();
+        let path = dir.path().join("module/src/main/kotlin/pkg");
+        let mut settings = ide_core::settings::Settings::default();
+        assert!(relevant_change(dir.path(), &path, &settings));
+        settings.project_structure.excluded.push("module/src/main/kotlin".into());
+        assert!(!relevant_change(dir.path(), &path, &settings));
+        assert!(!relevant_change(dir.path(), &dir.path().join("module/src/build/pkg"), &Default::default()));
+    }
+
+    #[test]
+    fn extensionless_root_file_does_not_trigger() {
+        let dir = tempfile::tempdir().unwrap();
+        std::fs::write(dir.path().join("pom.xml"), "").unwrap();
+        assert!(!relevant_change(dir.path(), &dir.path().join("LICENSE"), &Default::default()));
+    }
+
+    #[tokio::test(start_paused = true)]
+    async fn burst_saves_cancel_the_pending_debounce() {
+        let mut state = Revision::default();
+        state.change();
+        let token = state.cancel.clone();
+        let lifetime = CancellationToken::new();
+        let pending_lifetime = lifetime.clone();
+        let waiting = tokio::spawn(async move { debounce(&token, &pending_lifetime).await });
+        tokio::task::yield_now().await;
+        tokio::time::advance(DELAY - Duration::from_millis(1)).await;
+        assert!(!waiting.is_finished());
+        for _ in 0..20 {
+            state.change();
+        }
+        assert!(!waiting.await.unwrap());
+        let current = state.generation;
+        assert!(debounce(&state.cancel, &lifetime).await);
+        assert!(state.current(current));
+        lifetime.cancel();
+        assert!(!debounce(&state.cancel, &lifetime).await);
+    }
+
+    #[test]
+    fn superseded_and_cancelled_builds_cannot_publish() {
+        let mut state = Revision::default();
+        state.change();
+        let first = state.generation;
+        let token = state.cancel.clone();
+        state.change();
+        assert!(token.is_cancelled());
+        assert!(!state.current(first));
+        assert!(state.current(state.generation));
+        state.cancel.cancel();
+        assert!(!state.current(state.generation));
+    }
+}
diff --git a/crates/ide-host/src/lib.rs b/crates/ide-host/src/lib.rs
index ccb01db4a..5937b9725 100644
--- a/crates/ide-host/src/lib.rs
+++ b/crates/ide-host/src/lib.rs
@@ -4,7 +4,9 @@
 //! runs one on a remote machine and serves it over JSON-RPC ([`rpc`]).
 
 pub mod environment;
+mod formatter;
 mod java_runtime;
+mod kotlin_bridge;
 pub mod notebook;
 pub mod ops;
 mod project;
@@ -148,9 +150,15 @@ impl Host {
             if !project.light {
                 self.environment.project_closed();
             }
+            if let Some(bridge) = &project.kotlin_bridge {
+                bridge.stop();
+            }
             project.agents.shutdown();
             project.notebooks.stop_admission();
-            self.shutdown_notebooks_blocking(vec![project.notebooks.clone()]);
+            self.shutdown_project_workers_blocking(
+                vec![project.notebooks.clone()],
+                project.kotlin_bridge.iter().cloned().collect(),
+            );
             let lsp = project.lsp.clone();
             self.runtime.spawn(async move { lsp.shutdown_all().await });
         }
@@ -158,7 +166,14 @@ impl Host {
 
     /// Synchronous project/window destruction must finish owned kernel cleanup,
     /// not enqueue work which can be lost as the desktop runtime exits.
-    fn shutdown_notebooks_blocking(&self, notebooks: Vec<Arc<notebook::NotebookService>>) {
+    fn shutdown_project_workers_blocking(
+        &self,
+        notebooks: Vec<Arc<notebook::NotebookService>>,
+        bridges: Vec<Arc<kotlin_bridge::KotlinBridge>>,
+    ) {
+        for bridge in &bridges {
+            bridge.stop();
+        }
         for service in &notebooks {
             service.stop_admission();
         }
@@ -166,6 +181,9 @@ impl Host {
         let wait = move || {
             let worker = std::thread::spawn(move || {
                 runtime.block_on(async move {
+                    for bridge in bridges {
+                        bridge.shutdown().await;
+                    }
                     for service in notebooks {
                         service.shutdown().await;
                     }
@@ -186,7 +204,11 @@ impl Host {
 
     /// Called before the desktop runtime exits, including update/restart exits.
     pub fn shutdown_notebooks_on_exit(&self) {
-        self.shutdown_notebooks_blocking(self.projects().iter().map(|project| project.notebooks.clone()).collect());
+        let projects = self.projects();
+        self.shutdown_project_workers_blocking(
+            projects.iter().map(|project| project.notebooks.clone()).collect(),
+            projects.iter().filter_map(|project| project.kotlin_bridge.clone()).collect(),
+        );
     }
 
     /// Stops what this host started: notebook kernels, language servers, agents, runs and terminals.
@@ -197,12 +219,18 @@ impl Host {
         self.terminals.kill_all();
         let projects: Vec<_> = self.projects.write().drain().map(|(_, p)| p).collect();
         for project in &projects {
+            if let Some(bridge) = &project.kotlin_bridge {
+                bridge.stop();
+            }
             project.notebooks.stop_admission();
             project.agents.shutdown();
         }
         // Kernel cleanup owns its interrupt/termination/reaping deadlines. An
         // outer LSP timeout must never abort it before owned children are reaped.
         for project in &projects {
+            if let Some(bridge) = &project.kotlin_bridge {
+                bridge.shutdown().await;
+            }
             project.notebooks.shutdown().await;
         }
         let stop_language_servers = async {
diff --git a/crates/ide-host/src/ops/build.rs b/crates/ide-host/src/ops/build.rs
index 650db06d4..ad3983302 100644
--- a/crates/ide-host/src/ops/build.rs
+++ b/crates/ide-host/src/ops/build.rs
@@ -97,6 +97,7 @@ pub async fn build_sync(
     host.require_trust(window)?;
     let project = host.project(window)?;
     let (root, cache, settings) = (project.root.clone(), project.build_cache_dir(), project.settings.effective());
+    let bridge_profiles = profiles.clone();
     let token = host.begin_project_request(window, request);
     let result = tokio::task::spawn_blocking(move || {
         let current = load(&root, &cache, &settings);
@@ -137,6 +138,9 @@ pub async fn build_sync(
         // jdtls re-imports on pom changes but misses artifacts added to ~/.m2
         // meanwhile ("missing artifact" stays until Invalidate Caches); asking it
         // to update the project configurations re-resolves them (#436).
+        if let Some(bridge) = &project.kotlin_bridge {
+            bridge.configure_maven(offline, bridge_profiles);
+        }
         let lsp = project.lsp.clone();
         let uris = maven.projects.iter().map(|p| ide_lsp::path_to_uri_string(&project.root.join(&p.pom))).collect();
         tokio::spawn(async move {
diff --git a/crates/ide-host/src/ops/fs.rs b/crates/ide-host/src/ops/fs.rs
index 10681ca31..fb55f6f0f 100644
--- a/crates/ide-host/src/ops/fs.rs
+++ b/crates/ide-host/src/ops/fs.rs
@@ -1,8 +1,73 @@
+use super::Channel;
 use crate::Host;
-use ide_core::IdeResult;
+use ide_core::{IdeResult, RequestId};
 use ide_vfs::FileEntry;
 use std::path::PathBuf;
 
+pub async fn entry_kind(host: &Host, path: PathBuf) -> IdeResult<ide_vfs::EntryKind> {
+    host.blocking(move || {
+        let meta = std::fs::metadata(path)?;
+        Ok(if meta.is_dir() { ide_vfs::EntryKind::Dir } else { ide_vfs::EntryKind::File })
+    })
+    .await
+}
+
+pub async fn compare_directories(
+    host: &Host,
+    window: &str,
+    left: PathBuf,
+    right: PathBuf,
+    request: RequestId,
+    on_progress: Channel<ide_vfs::DirectoryCompareProgress>,
+) -> IdeResult<Vec<ide_vfs::DirectoryCompareEntry>> {
+    let project = host.project(window)?;
+    let cancel = host.begin_request(request);
+    let result = host
+        .blocking(move || {
+            let last = std::cell::Cell::new(std::time::Instant::now() - std::time::Duration::from_secs(1));
+            ide_vfs::compare_directories(&left, &right, Some(&project.root), &project.exclude_globs(), &cancel, |p| {
+                // Bound IPC traffic even when hashing multi-gigabyte files.
+                if last.get().elapsed() >= std::time::Duration::from_millis(80) || p.total == Some(p.compared) {
+                    let _ = on_progress.send(p);
+                    last.set(std::time::Instant::now());
+                }
+            })
+        })
+        .await;
+    host.end_request(request);
+    result
+}
+
+pub async fn copy_merge(
+    host: &Host,
+    window: &str,
+    source_root: PathBuf,
+    destination_root: PathBuf,
+    path: PathBuf,
+    overwrite: bool,
+) -> IdeResult<()> {
+    if path.as_os_str().is_empty() || path.components().any(|c| !matches!(c, std::path::Component::Normal(_))) {
+        return Err(ide_core::IdeError::invalid("expected a relative comparison entry path"));
+    }
+    let project = host.project(window)?;
+    host.blocking(move || {
+        let from = source_root.join(&path);
+        let to = destination_root.join(&path);
+        if overwrite {
+            project.history.record_deletion(&to, DELETE_SNAPSHOT_LIMIT);
+        }
+        ide_vfs::copy_merge(
+            &from,
+            &to,
+            overwrite,
+            Some(&project.root),
+            &project.exclude_globs(),
+            (&source_root, &destination_root),
+        )
+    })
+    .await
+}
+
 /// Files of a deleted folder snapshotted in Local History.
 const DELETE_SNAPSHOT_LIMIT: usize = 2000;
 
diff --git a/crates/ide-host/src/ops/java.rs b/crates/ide-host/src/ops/java.rs
index 4eccfb01f..47beb38d5 100644
--- a/crates/ide-host/src/ops/java.rs
+++ b/crates/ide-host/src/ops/java.rs
@@ -1,11 +1,13 @@
 //! Java launch support: classpath / JDK resolution and the java-debug server (jdtls).
+pub(crate) mod cache;
+
 use crate::Host;
 use crate::rpc::Dispatcher;
 
 use super::build::load;
 use ide_build::compile;
 use ide_core::{CancellationToken, IdeError, IdeResult, RequestId};
-use ide_lsp::jdtls::JavaLaunchInfo;
+use ide_lsp::jdtls::{JavaBuildStatus, JavaLaunchInfo};
 use std::path::PathBuf;
 
 /// Cancellable with `cancel_request(request)`.
@@ -39,20 +41,46 @@ async fn resolve_launch(
     let project = host.project(window)?;
     let module = project.root.join(module);
     let settings = project.settings.effective();
-    // Let jdtls finish its build before the external compiler writes Kotlin/Scala classes.
-    let mut info = project.lsp.java_launch(&module, test, build, cancel).await?;
+    let (model, external, delegated) = {
+        let project = project.clone();
+        let settings = settings.clone();
+        let module = module.clone();
+        tokio::task::spawn_blocking(move || {
+            project.java_launch_snapshots.lock().initialize();
+            let model = load(&project.root, &project.build_cache_dir(), &settings);
+            let non_java = build && compile::launch_has_non_java_sources(&project.root, &model, &module, test);
+            let delegated = build
+                && model.maven.as_ref().is_some_and(|m| m.projects.iter().any(|p| project.root.join(&p.dir) == module))
+                && (non_java || cache::has_record(&project.root, &project.build_cache_dir(), &module));
+            let external = non_java || delegated;
+            (model, external, delegated)
+        })
+        .await
+        .map_err(|e| IdeError::internal(e.to_string()))?
+    };
+    let external_build = if delegated { Some(project.lsp.java_external_build(&module, cancel).await?) } else { None };
+    let mut info = project.lsp.java_launch(&module, test, build && !delegated, cancel).await?;
     let lsp_ms = started.elapsed().as_millis();
     let data_dir = host.data_dir.clone();
     let cancel = cancel.clone();
     tokio::task::spawn_blocking(move || {
-        let built = if build && compile::has_non_java_sources(&module) {
-            compile::build_for_launch(
+        let _external_build = external_build;
+        let built = if delegated {
+            let outputs = project.java_launch_snapshots.lock().build(
                 &project.root,
-                &load(&project.root, &project.build_cache_dir(), &settings),
+                &model,
                 &module,
                 test,
+                ide_sdk::apply::maven_local_repository(&project.root, &settings),
                 &cancel,
-            )?
+            )?;
+            let copies = use_snapshot(&mut info, &outputs.originals, &outputs.snapshot);
+            info.build = Some(JavaBuildStatus::Succeeded);
+            info.errors.clear();
+            info.error_count = 0;
+            copies
+        } else if external {
+            compile::build_for_launch(&project.root, &model, &module, test, &cancel)?
         } else {
             Vec::new()
         };
@@ -103,6 +131,26 @@ async fn resolve_launch(
     .map_err(|e| IdeError::internal(e.to_string()))?
 }
 
+fn use_snapshot(info: &mut JavaLaunchInfo, built: &[PathBuf], snapshot: &std::path::Path) -> Vec<PathBuf> {
+    let mut copies = Vec::new();
+    for (index, source) in built.iter().enumerate() {
+        let dest = snapshot.join(index.to_string());
+        let original = source.to_string_lossy();
+        info.class_paths.retain(|p| p != original.as_ref());
+        let mut modular = false;
+        for path in &mut info.module_paths {
+            if path == original.as_ref() {
+                *path = dest.to_string_lossy().into_owned();
+                modular = true;
+            }
+        }
+        if !modular {
+            copies.push(dest);
+        }
+    }
+    copies
+}
+
 /// Port of java-debug's DAP server inside the jdtls serving `module` (started on demand).
 pub async fn java_debug_server(host: &Host, window: &str, module: PathBuf) -> IdeResult<u16> {
     host.require_trust(window)?;
@@ -132,3 +180,40 @@ pub(crate) fn register(d: &mut Dispatcher) {
     d.add("java_debug_server", |c| async move { java_debug_server(&c.host, &c.window, c.arg("module")?).await });
     d.add("java_build_workspace", |c| async move { java_build_workspace(&c.host, &c.window, c.arg("module")?).await });
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn launch_snapshots_survive_jdt_overwrites_and_replace_module_outputs() {
+        let root = tempfile::tempdir().unwrap();
+        let app = root.path().join("app/target/classes");
+        let lib = root.path().join("lib/target/classes");
+        for dir in [&app, &lib] {
+            std::fs::create_dir_all(dir).unwrap();
+            std::fs::write(dir.join("Channel.class"), "Maven bytecode").unwrap();
+        }
+        let mut info = JavaLaunchInfo {
+            class_paths: vec![app.to_string_lossy().into_owned(), "stdlib.jar".into()],
+            module_paths: vec![lib.to_string_lossy().into_owned()],
+            ..Default::default()
+        };
+        let snapshot = tempfile::tempdir().unwrap();
+        for (i, source) in [&app, &lib].iter().enumerate() {
+            ide_vfs::copy(source, &snapshot.path().join(i.to_string())).unwrap();
+        }
+        let paths = use_snapshot(&mut info, &[app.clone(), lib.clone()], snapshot.path());
+        assert_eq!(paths, [snapshot.path().join("0")]);
+        assert_eq!(info.class_paths, ["stdlib.jar"]);
+        assert_eq!(info.module_paths, [snapshot.path().join("1").to_string_lossy().into_owned()]);
+        std::fs::write(app.join("Channel.class"), "JDT error stub").unwrap();
+        std::fs::remove_dir_all(lib).unwrap();
+        for index in ["0", "1"] {
+            assert_eq!(
+                std::fs::read_to_string(snapshot.path().join(index).join("Channel.class")).unwrap(),
+                "Maven bytecode"
+            );
+        }
+    }
+}
diff --git a/crates/ide-host/src/ops/java/cache.rs b/crates/ide-host/src/ops/java/cache.rs
new file mode 100644
index 000000000..422ade156
--- /dev/null
+++ b/crates/ide-host/src/ops/java/cache.rs
@@ -0,0 +1,371 @@
+//! Immutable Maven outputs retained in the project cache, including across close/reopen.
+use ide_build::compile::{self, LaunchFingerprint};
+use ide_core::{CancellationToken, IdeError, IdeResult};
+use serde::{Deserialize, Serialize};
+use std::collections::HashSet;
+use std::fs;
+use std::path::{Path, PathBuf};
+
+#[derive(Debug, Serialize, Deserialize)]
+pub(super) struct Outputs {
+    fingerprint: Option<LaunchFingerprint>,
+    pub snapshot: PathBuf,
+    pub originals: Vec<PathBuf>,
+}
+
+impl Outputs {
+    fn reusable(&self, fingerprint: &Option<LaunchFingerprint>, snapshots: &Path) -> bool {
+        fingerprint.is_some()
+            && self.fingerprint == *fingerprint
+            && self.snapshot.parent() == Some(snapshots)
+            && !self.originals.is_empty()
+            && (0..self.originals.len()).all(|i| self.snapshot.join(i.to_string()).is_dir())
+    }
+}
+
+fn record_path(root: &Path, cache: &Path, module: &Path, test: bool) -> Option<PathBuf> {
+    Some(cache.join("java-launch/records").join(module.strip_prefix(root).ok()?).join(if test {
+        "test.json"
+    } else {
+        "main.json"
+    }))
+}
+
+pub(super) fn has_record(root: &Path, cache: &Path, module: &Path) -> bool {
+    [false, true].into_iter().any(|test| record_path(root, cache, module, test).is_some_and(|record| record.is_file()))
+}
+
+/// Owned by Project: running JVMs may still load superseded outputs until it drops.
+pub(crate) struct Session {
+    cache: PathBuf,
+    initialized: bool,
+    unreferenced: Vec<PathBuf>,
+}
+
+impl Session {
+    pub(crate) fn new(cache: PathBuf) -> Self {
+        Self { cache, initialized: false, unreferenced: Vec::new() }
+    }
+
+    pub(super) fn initialize(&mut self) {
+        if !self.initialized {
+            self.initialized = true;
+            if let Err(error) = sweep(&self.cache) {
+                tracing::warn!(%error, "Cannot clean previous Java launch snapshots");
+            }
+        }
+    }
+
+    pub(super) fn build(
+        &mut self,
+        root: &Path,
+        model: &ide_build::BuildModel,
+        module: &Path,
+        test: bool,
+        local_repo: Option<PathBuf>,
+        cancel: &CancellationToken,
+    ) -> IdeResult<Outputs> {
+        self.initialize();
+        let cache = &self.cache;
+        let record =
+            record_path(root, cache, module, test).ok_or_else(|| IdeError::internal("launch outside project"))?;
+        let snapshots = cache.join("java-launch/snapshots");
+        let fingerprint = || match compile::launch_fingerprint(root, model, module, test, local_repo.clone(), cancel) {
+            Ok(value) => Ok(value),
+            Err(e) if cancel.is_cancelled() => Err(e),
+            Err(e) => {
+                tracing::debug!(error = %e, "Cannot fingerprint Maven launch; rebuilding");
+                Ok(None)
+            }
+        };
+        let before = fingerprint()?;
+        let previous = fs::read(&record).ok().and_then(|bytes| serde_json::from_slice::<Outputs>(&bytes).ok());
+        if let Some(outputs) = previous.as_ref()
+            && outputs.reusable(&before, &snapshots)
+        {
+            tracing::info!(module = %module.display(), test, "Reusing Maven launch snapshot");
+            return Ok(previous.unwrap());
+        }
+        // Retain a non-reusable record even on failure, so removing the final mixed
+        // source still delegates to Maven to clean its old classes on the next launch.
+        fs::create_dir_all(record.parent().unwrap())?;
+        fs::write(&record, b"null")?;
+        if let Some(previous) = previous {
+            self.unreferenced.push(previous.snapshot);
+        }
+        let originals = compile::build_for_launch(root, model, module, test, cancel)?;
+        fs::create_dir_all(&snapshots)?;
+        let snapshot = tempfile::Builder::new().prefix("launch-").tempdir_in(&snapshots)?.keep();
+        // Retain every new snapshot even if copying or publishing its record fails.
+        self.unreferenced.push(snapshot.clone());
+        for (i, source) in originals.iter().enumerate() {
+            if cancel.is_cancelled() {
+                return Err(IdeError::cancelled());
+            }
+            ide_vfs::copy(source, &snapshot.join(i.to_string()))?;
+        }
+        let after = fingerprint()?;
+        if cancel.is_cancelled() {
+            return Err(IdeError::cancelled());
+        }
+        let mut outputs = Outputs { fingerprint: None, snapshot, originals };
+        if before.is_some() && before == after {
+            outputs.fingerprint = before;
+            fs::create_dir_all(record.parent().unwrap())?;
+            let mut file = tempfile::NamedTempFile::new_in(record.parent().unwrap())?;
+            serde_json::to_writer(file.as_file_mut(), &outputs).map_err(|e| IdeError::internal(e.to_string()))?;
+            file.persist(&record).map_err(|e| IdeError::from(e.error))?;
+            self.unreferenced.retain(|path| path != &outputs.snapshot);
+        }
+        Ok(outputs)
+    }
+}
+
+impl Drop for Session {
+    fn drop(&mut self) {
+        // Recheck all records: another module or launch mode may reference a path.
+        if let Ok(referenced) = referenced_snapshots(&self.cache) {
+            let snapshots = self.cache.join("java-launch/snapshots");
+            for path in &self.unreferenced {
+                remove_unreferenced(path, &snapshots, &referenced);
+            }
+        }
+    }
+}
+
+fn referenced_snapshots(cache: &Path) -> std::io::Result<HashSet<PathBuf>> {
+    let mut referenced = HashSet::new();
+    let records = cache.join("java-launch/records");
+    if !records.try_exists()? {
+        return Ok(referenced);
+    }
+    let mut pending = vec![records];
+    while let Some(dir) = pending.pop() {
+        for entry in fs::read_dir(dir)? {
+            let entry = entry?;
+            let kind = entry.file_type()?;
+            if kind.is_dir() {
+                pending.push(entry.path());
+            } else if kind.is_file() && entry.path().extension().is_some_and(|ext| ext == "json") {
+                let outputs: Option<Outputs> = serde_json::from_slice(&fs::read(entry.path())?)?;
+                if let Some(outputs) = outputs
+                    && let Ok(path) = fs::canonicalize(outputs.snapshot)
+                {
+                    referenced.insert(path);
+                }
+            }
+        }
+    }
+    Ok(referenced)
+}
+
+fn remove_unreferenced(path: &Path, snapshots: &Path, referenced: &HashSet<PathBuf>) {
+    // Only real launch-* directories directly inside snapshots, never symlinks.
+    if path.parent() != Some(snapshots)
+        || !path.file_name().is_some_and(|name| name.to_string_lossy().starts_with("launch-"))
+        || !fs::symlink_metadata(path).is_ok_and(|meta| meta.file_type().is_dir())
+    {
+        return;
+    }
+    if let (Ok(path), Ok(snapshots)) = (fs::canonicalize(path), fs::canonicalize(snapshots))
+        && path.parent() == Some(snapshots.as_path())
+        && !referenced.contains(&path)
+        && let Err(error) = fs::remove_dir_all(&path)
+    {
+        tracing::warn!(%error, path = %path.display(), "Cannot remove Java launch snapshot");
+    }
+}
+
+fn sweep(cache: &Path) -> std::io::Result<()> {
+    let referenced = referenced_snapshots(cache)?;
+    let snapshots = cache.join("java-launch/snapshots");
+    if snapshots.try_exists()? {
+        for entry in fs::read_dir(&snapshots)? {
+            remove_unreferenced(&entry?.path(), &snapshots, &referenced);
+        }
+    }
+    Ok(())
+}
+
+#[cfg(all(test, unix))]
+mod tests {
+    use super::*;
+    use std::os::unix::fs::PermissionsExt;
+
+    fn fixture(root: &Path) -> ide_build::BuildModel {
+        fs::write(
+            root.join("pom.xml"),
+            r#"<project><groupId>demo</groupId><artifactId>app</artifactId><version>1</version></project>"#,
+        )
+        .unwrap();
+        let script = root.join("mvnw");
+        fs::write(&script, "#!/bin/sh\necho build >> calls\nif [ -f src/main/kotlin/broken ]; then exit 1; fi\nmkdir -p target/classes\ncp src/main/kotlin/Main.kt target/classes/Main.class\n").unwrap();
+        fs::set_permissions(&script, fs::Permissions::from_mode(0o755)).unwrap();
+        fs::create_dir_all(root.join("src/main/kotlin")).unwrap();
+        fs::write(root.join("src/main/kotlin/Main.kt"), "first").unwrap();
+        ide_build::load(root, &root.join("cache"), None)
+    }
+
+    #[test]
+    fn successful_snapshots_reuse_across_close_and_rebuild_for_changes_missing_outputs_or_failure() {
+        let dir = tempfile::tempdir().unwrap();
+        let root = dir.path();
+        let model = fixture(root);
+        let cache = root.join("cache");
+        let cancel = CancellationToken::new();
+        let mut session = Session::new(cache.clone());
+        let mut build = || session.build(root, &model, root, false, None, &cancel);
+        let first = build().unwrap();
+        let snapshot = first.snapshot.clone();
+        drop(first);
+        // Dropping an Outputs value leaves the persisted snapshot reusable.
+        let second = build().unwrap();
+        assert_eq!(snapshot, second.snapshot);
+        assert_eq!(fs::read_to_string(root.join("calls")).unwrap().lines().count(), 1);
+        fs::write(root.join("target/classes/Main.class"), "JDT stub").unwrap();
+        assert_eq!(snapshot, build().unwrap().snapshot);
+        assert_eq!(fs::read_to_string(snapshot.join("0/Main.class")).unwrap(), "first");
+        fs::write(root.join("src/main/kotlin/Main.kt"), "updated").unwrap();
+        let updated = build().unwrap();
+        assert_ne!(snapshot, updated.snapshot);
+        assert_eq!(fs::read_to_string(updated.snapshot.join("0/Main.class")).unwrap(), "updated");
+        assert!(snapshot.join("0/Main.class").is_file(), "previous JVMs may still load it");
+        fs::remove_dir_all(updated.snapshot.join("0")).unwrap();
+        let rebuilt = build().unwrap();
+        assert_ne!(rebuilt.snapshot, updated.snapshot);
+        fs::write(root.join("src/main/kotlin/broken"), "broken").unwrap();
+        assert!(build().is_err());
+        assert_eq!(fs::read(cache.join("java-launch/records/main.json")).unwrap(), b"null");
+        fs::remove_file(root.join("src/main/kotlin/broken")).unwrap();
+        assert_ne!(rebuilt.snapshot, build().unwrap().snapshot, "a failed build invalidates success");
+        cancel.cancel();
+        assert!(build().is_err());
+        assert_eq!(fs::read_to_string(root.join("calls")).unwrap().lines().count(), 5);
+    }
+    #[test]
+    fn session_drop_removes_superseded_snapshots_and_preserves_records_across_reopen() {
+        let dir = tempfile::tempdir().unwrap();
+        let root = dir.path();
+        let model = fixture(root);
+        let cache = root.join("cache");
+        let cancel = CancellationToken::new();
+        let mut session = Session::new(cache.clone());
+        let first = session.build(root, &model, root, false, None, &cancel).unwrap();
+        fs::write(root.join("src/main/kotlin/Main.kt"), "updated").unwrap();
+        let second = session.build(root, &model, root, false, None, &cancel).unwrap();
+        assert!(first.snapshot.is_dir());
+        assert!(second.snapshot.is_dir());
+        // Another mode can keep a superseded snapshot alive.
+        let test_record = cache.join("java-launch/records/nested/test.json");
+        fs::create_dir_all(test_record.parent().unwrap()).unwrap();
+        fs::write(&test_record, serde_json::to_vec(&first).unwrap()).unwrap();
+        drop(session);
+        assert!(first.snapshot.is_dir());
+        assert!(second.snapshot.is_dir());
+        let mut session = Session::new(cache.clone());
+        let reused = session.build(root, &model, root, false, None, &cancel).unwrap();
+        assert_eq!(reused.snapshot, second.snapshot);
+        fs::write(root.join("src/main/kotlin/Main.kt"), "third version").unwrap();
+        let third = session.build(root, &model, root, false, None, &cancel).unwrap();
+        assert!(second.snapshot.is_dir());
+        drop(session);
+        assert!(!second.snapshot.exists());
+        assert!(first.snapshot.is_dir());
+        assert!(third.snapshot.is_dir());
+        assert_eq!(fs::read_to_string(root.join("calls")).unwrap().lines().count(), 3);
+    }
+
+    #[test]
+    fn initial_sweep_only_removes_unreferenced_direct_snapshot_directories() {
+        let dir = tempfile::tempdir().unwrap();
+        let cache = dir.path().join("cache");
+        let snapshots = cache.join("java-launch/snapshots");
+        let retained = snapshots.join("launch-retained");
+        let orphan = snapshots.join("launch-orphan");
+        let other = snapshots.join("other");
+        let nested = other.join("launch-nested");
+        let outside = dir.path().join("launch-outside");
+        for path in [&retained, &orphan, &nested, &outside] {
+            fs::create_dir_all(path).unwrap();
+        }
+        fs::write(outside.join("classes"), "keep").unwrap();
+        std::os::unix::fs::symlink(&outside, snapshots.join("launch-link")).unwrap();
+        fs::write(snapshots.join("launch-file"), "keep").unwrap();
+        let record = cache.join("java-launch/records/deep/module/test.json");
+        fs::create_dir_all(record.parent().unwrap()).unwrap();
+        let outputs = Outputs { fingerprint: None, snapshot: retained.clone(), originals: Vec::new() };
+        fs::write(record, serde_json::to_vec(&outputs).unwrap()).unwrap();
+        let mut session = Session::new(cache);
+        session.initialize();
+        assert!(!orphan.exists());
+        assert!(retained.is_dir());
+        assert!(nested.is_dir());
+        assert!(outside.join("classes").is_file());
+        assert!(snapshots.join("launch-link").is_symlink());
+        assert!(snapshots.join("launch-file").is_file());
+        // Initialization must not sweep snapshots still in use by this session.
+        fs::create_dir_all(&orphan).unwrap();
+        session.initialize();
+        assert!(orphan.is_dir());
+        session.unreferenced.extend([outside.clone(), snapshots.join("../../launch-outside"), nested]);
+        drop(session);
+        assert!(outside.join("classes").is_file());
+        assert!(other.join("launch-nested").is_dir());
+    }
+
+    #[test]
+    fn failed_record_publish_retains_snapshot_until_session_drop() {
+        let dir = tempfile::tempdir().unwrap();
+        let root = dir.path();
+        let model = fixture(root);
+        let script = root.join("mvnw");
+        let mut text = fs::read_to_string(&script).unwrap();
+        text.push_str("rm cache/java-launch/records/main.json\nmkdir cache/java-launch/records/main.json\n");
+        fs::write(script, text).unwrap();
+        let cache = root.join("cache");
+        let mut session = Session::new(cache.clone());
+        assert!(session.build(root, &model, root, false, None, &CancellationToken::new()).is_err());
+        assert_eq!(session.unreferenced.len(), 1);
+        let snapshot = session.unreferenced[0].clone();
+        assert!(snapshot.join("0/Main.class").is_file());
+        drop(session);
+        assert!(!snapshot.exists());
+    }
+
+    #[test]
+    fn edits_during_build_do_not_publish_a_success_record() {
+        let dir = tempfile::tempdir().unwrap();
+        let root = dir.path();
+        let model = fixture(root);
+        let script = root.join("mvnw");
+        let mut text = fs::read_to_string(&script).unwrap();
+        text.push_str("echo edited-during-build >> src/main/kotlin/Main.kt\n");
+        fs::write(script, text).unwrap();
+        let cache = root.join("cache");
+        let mut session = Session::new(cache.clone());
+        let outputs = session.build(root, &model, root, false, None, &CancellationToken::new()).unwrap();
+        assert!(outputs.fingerprint.is_none());
+        assert_eq!(fs::read(cache.join("java-launch/records/main.json")).unwrap(), b"null");
+        assert!(outputs.snapshot.join("0/Main.class").is_file());
+        drop(session);
+        assert!(!outputs.snapshot.exists());
+    }
+    #[test]
+    fn deleting_the_last_mixed_source_keeps_maven_delegation_after_failure() {
+        let dir = tempfile::tempdir().unwrap();
+        let root = dir.path();
+        let model = fixture(root);
+        let cache = root.join("cache");
+        let cancel = CancellationToken::new();
+        let mut session = Session::new(cache.clone());
+        let first = session.build(root, &model, root, false, None, &cancel).unwrap();
+        fs::remove_file(root.join("src/main/kotlin/Main.kt")).unwrap();
+        assert!(!compile::launch_has_non_java_sources(root, &model, root, false));
+        assert!(has_record(root, &cache, root));
+        assert!(session.build(root, &model, root, false, None, &cancel).is_err());
+        assert!(has_record(root, &cache, root));
+        fs::write(root.join("src/main/kotlin/Main.kt"), "restored").unwrap();
+        let restored = session.build(root, &model, root, false, None, &cancel).unwrap();
+        assert_ne!(first.snapshot, restored.snapshot);
+    }
+}
diff --git a/crates/ide-host/src/ops/lsp.rs b/crates/ide-host/src/ops/lsp.rs
index 953f878a7..b57f54efd 100644
--- a/crates/ide-host/src/ops/lsp.rs
+++ b/crates/ide-host/src/ops/lsp.rs
@@ -83,12 +83,18 @@ pub async fn lsp_implementations(
     result
 }
 
-/// Contents of a virtual document (library class, decompiled code) that a
-/// language server returned a non-`file:` URI for. Cached per project.
+/// Contents of a read-only language-server document, including JDT library
+/// classes and disk class files. Cached per project.
 pub async fn lsp_virtual_document(host: &Host, window: &str, uri: String) -> IdeResult<VirtualDocument> {
     host.project(window)?.lsp.virtual_document(&uri).await
 }
 
+/// Opens compiled classes through JDT, with project source taking priority on disk.
+pub async fn lsp_resolve_class_file(host: &Host, window: &str, path: std::path::PathBuf) -> IdeResult<String> {
+    let archive = ide_vfs::split_archive_path(&path);
+    host.project(window)?.lsp.java_class_file(&path, archive).await
+}
+
 /// References of the symbol at `pos`. `project_wide` also searches project files
 /// outside the language server's analysis scope; bulk scans over many symbols
 /// leave it off. Cancel with `cancel_request(request)`.
@@ -208,7 +214,7 @@ pub async fn lsp_format(
     range: Option<Range>,
     options: FormatOptions,
 ) -> IdeResult<Vec<TextEdit>> {
-    host.project(window)?.lsp.format(doc, range, options).await
+    crate::formatter::format(host, window, doc, range, options).await
 }
 
 pub async fn lsp_inlay_hints(host: &Host, window: &str, doc: DocId, range: Range) -> IdeResult<Vec<InlayHint>> {
@@ -263,7 +269,13 @@ pub fn lsp_resend_diagnostics(host: &Host, window: &str) -> IdeResult<()> {
 }
 
 pub async fn lsp_restart(host: &Host, window: &str, server: ServerId) -> IdeResult<()> {
-    host.project(window)?.lsp.restart(server).await
+    let project = host.project(window)?;
+    let java = project.lsp.servers().iter().any(|s| s.id == server && s.name == "jdtls");
+    project.lsp.restart(server).await?;
+    if java && let Some(bridge) = &project.kotlin_bridge {
+        bridge.schedule();
+    }
+    Ok(())
 }
 
 /// Applies a (previewed) workspace edit, e.g. after rename confirmation.
@@ -367,6 +379,10 @@ pub(crate) fn register(d: &mut Dispatcher) {
     d.add("lsp_implementations", |c| async move {
         lsp_implementations(&c.host, &c.window, c.arg("request")?, c.arg("doc")?, c.arg("positions")?).await
     });
+    d.add(
+        "lsp_resolve_class_file",
+        |c| async move { lsp_resolve_class_file(&c.host, &c.window, c.arg("path")?).await },
+    );
     d.add("lsp_virtual_document", |c| async move { lsp_virtual_document(&c.host, &c.window, c.arg("uri")?).await });
     d.add("lsp_references", |c| async move {
         lsp_references(
diff --git a/crates/ide-host/src/ops/project.rs b/crates/ide-host/src/ops/project.rs
index ec1d44026..4c17cdde1 100644
--- a/crates/ide-host/src/ops/project.rs
+++ b/crates/ide-host/src/ops/project.rs
@@ -177,6 +177,9 @@ pub fn set_settings(
         .any(|k| key == *k || key.starts_with(&format!("{k}.")))
     {
         for project in affected() {
+            if let Some(bridge) = &project.kotlin_bridge {
+                bridge.schedule();
+            }
             let lsp = project.lsp.clone();
             host.runtime.spawn(async move { lsp.reconfigure().await });
         }
diff --git a/crates/ide-host/src/ops/term.rs b/crates/ide-host/src/ops/term.rs
index 20393ead2..50d8ac8cc 100644
--- a/crates/ide-host/src/ops/term.rs
+++ b/crates/ide-host/src/ops/term.rs
@@ -16,11 +16,15 @@ pub fn spawn(
         options.args.clear();
         options.env = global.env;
     }
-    // Python › "Activate virtualenv": typed into the new shell, like PyCharm.
-    let activation =
-        host.project(window).ok().filter(|p| p.is_trusted()).and_then(|p| {
-            ide_sdk::apply::terminal_activation(&p.root, &p.settings.effective(), options.shell.as_deref())
-        });
+    let (shell, args) = ide_terminal::resolve_shell(options.shell.as_deref(), &options.args);
+    options.shell = Some(shell.clone());
+    options.args = args;
+    // Python › "Activate virtualenv": typed into the same shell the PTY starts.
+    let activation = host
+        .project(window)
+        .ok()
+        .filter(|p| p.is_trusted())
+        .and_then(|p| ide_sdk::apply::terminal_activation(&p.root, &p.settings.effective(), &shell));
     let info = host.terminals.spawn(options, host.window_sink(window), Box::new(move |chunk| on_output(chunk)))?;
     if let Some(line) = activation {
         let _ = host.terminals.write(info.id, &format!(" {line}\r"));
diff --git a/crates/ide-host/src/ops/tools.rs b/crates/ide-host/src/ops/tools.rs
index f87b5799c..f8f05b1ff 100644
--- a/crates/ide-host/src/ops/tools.rs
+++ b/crates/ide-host/src/ops/tools.rs
@@ -100,11 +100,11 @@ pub fn jdk_download_vendors(_host: &Host, _window: &str) -> Vec<JdkVendor> {
 /// Java versions `vendor` publishes; cancellable with `cancel_request(request)`.
 pub async fn jdk_download_releases(
     host: &Host,
-    window: &str,
+    _window: &str,
     vendor: String,
     request: RequestId,
 ) -> IdeResult<JdkReleases> {
-    let tools = tools(host, window)?;
+    let tools = Tools::new(&host.data_dir);
     let cancel = host.begin_request(request);
     let result = tokio::task::spawn_blocking(move || tools.jdk_releases(&vendor, &cancel)).await.map_err(join_err);
     host.end_request(request);
@@ -123,14 +123,14 @@ pub fn jdk_download_location(host: &Host, _window: &str) -> IdeResult<ide_core::
 #[allow(clippy::too_many_arguments)]
 pub async fn jdk_download(
     host: &Host,
-    window: &str,
+    _window: &str,
     vendor: String,
     version: u32,
     location: Option<PathBuf>,
     request: RequestId,
     on_event: Channel<InstallEvent>,
 ) -> IdeResult<Sdk> {
-    let tools = tools(host, window)?;
+    let tools = Tools::new(&host.data_dir);
     let location = location.filter(|p| !p.as_os_str().is_empty());
     let cancel = host.begin_request(request);
     let result = tokio::task::spawn_blocking(move || {
diff --git a/crates/ide-host/src/project.rs b/crates/ide-host/src/project.rs
index 24cc4aa34..f28c7cffe 100644
--- a/crates/ide-host/src/project.rs
+++ b/crates/ide-host/src/project.rs
@@ -42,6 +42,8 @@ pub struct Project {
     pub detected_roots: Arc<RwLock<Vec<SourceFolder>>>,
     /// Per-project cache directory (build tool sync results…).
     pub cache_dir: PathBuf,
+    /// Superseded launch snapshots retained until this project session ends.
+    pub(crate) java_launch_snapshots: Mutex<crate::ops::java::cache::Session>,
     /// Database tool window: data sources and their connections.
     pub db: Arc<ide_db::DbManager>,
     /// HTTP Client responses (IDEA's `.idea/httpRequests`), in the app data dir.
@@ -50,6 +52,7 @@ pub struct Project {
     pub agents: Arc<ide_agent::AgentManager>,
     /// Native notebooks and owned kernels, scoped to this project incarnation.
     pub notebooks: Arc<crate::notebook::NotebookService>,
+    pub(crate) kotlin_bridge: Option<Arc<crate::kotlin_bridge::KotlinBridge>>,
     pub(crate) watcher: Watcher,
     /// Watchers of the Project Structure content roots outside the project folder.
     pub(crate) content_watchers: Mutex<Vec<(PathBuf, Watcher)>>,
@@ -150,6 +153,7 @@ impl Host {
                     let bundles: Vec<PathBuf> = ide_tools::managed_bundle(&data_dir, "java-debug")
                         .into_iter()
                         .chain(ide_sdk::java::usages_bundle(&data_dir))
+                        .chain(ide_sdk::java::kotlin_bridge_bundle(&data_dir))
                         .collect();
                     let min_java = ide_sdk::java::jdtls_min_java(cfg);
                     let jdks = ide_sdk::java::jdtls_jdks(min_java, &data_dir);
@@ -226,11 +230,22 @@ impl Host {
             trusted: trusted.clone(),
         }));
 
+        let kotlin_bridge = crate::kotlin_bridge::KotlinBridge::new(
+            root.clone(),
+            self.data_dir.join("cache").join(&project_key).join("build"),
+            &self.data_dir,
+            settings.clone(),
+            lsp.clone(),
+            sink.clone(),
+            trusted.clone(),
+        );
+        documents.add_observer(kotlin_bridge.clone());
         let repos = Arc::new(RwLock::new(Repos::enclosing(&root)?));
         for repo in repos.read().all() {
             repo.set_execution_allowed(trusted.load(Ordering::Acquire));
         }
         let watcher = {
+            let kotlin_bridge = kotlin_bridge.clone();
             let repos = repos.clone();
             let settings = settings.clone();
             let index = index.clone();
@@ -251,6 +266,7 @@ impl Host {
                 Box::new(move |batch| {
                     let changed: Vec<PathBuf> = batch.created.iter().chain(&batch.modified).cloned().collect();
                     index.update(&changed, &batch.removed);
+                    kotlin_bridge.files_changed(changed.iter().chain(&batch.removed));
                     lsp.project_files_changed(batch.created.iter().chain(&batch.removed));
                     // Atomic saves by external tools surface as `created`.
                     documents.on_disk_changed(&changed);
@@ -330,7 +346,7 @@ impl Host {
         let content_watchers = extra_roots
             .iter()
             .filter_map(|r| {
-                let w = content_root_watcher(r, &excludes, &sink, &index, &documents, &history)?;
+                let w = content_root_watcher(r, &excludes, &sink, &index, &documents, &history, Some(&kotlin_bridge))?;
                 Some((r.clone(), w))
             })
             .collect();
@@ -366,10 +382,14 @@ impl Host {
             syntax,
             detected_roots,
             cache_dir: self.data_dir.join("cache").join(&project_key),
+            java_launch_snapshots: Mutex::new(crate::ops::java::cache::Session::new(
+                self.data_dir.join("cache").join(&project_key).join("build"),
+            )),
             db,
             http_history,
             agents,
             notebooks,
+            kotlin_bridge: Some(kotlin_bridge),
             watcher,
             content_watchers: Mutex::new(content_watchers),
             _scratch_watcher: scratch_watcher,
@@ -388,6 +408,9 @@ impl Host {
             }));
         }
         self.insert_project(window, project.clone());
+        if let Some(bridge) = &project.kotlin_bridge {
+            bridge.start(&self.runtime);
+        }
         if let Some(cmd) = post_start {
             self.environment.spawn_post_start(cmd, project.root.clone(), project.sink.clone());
         }
@@ -481,10 +504,14 @@ impl Host {
             syntax,
             detected_roots: Arc::default(),
             cache_dir: self.data_dir.join("cache").join(&project_key),
+            java_launch_snapshots: Mutex::new(crate::ops::java::cache::Session::new(
+                self.data_dir.join("cache").join(&project_key).join("build"),
+            )),
             db,
             http_history,
             agents,
             notebooks,
+            kotlin_bridge: None,
             watcher,
             content_watchers: Mutex::new(Vec::new()),
             _scratch_watcher: None,
@@ -778,9 +805,15 @@ impl Project {
             if watchers.iter().any(|(p, _)| *p == r) {
                 continue;
             }
-            if let Some(w) =
-                content_root_watcher(&r, &excludes, &self.sink, &self.index, &self.documents, &self.history)
-            {
+            if let Some(w) = content_root_watcher(
+                &r,
+                &excludes,
+                &self.sink,
+                &self.index,
+                &self.documents,
+                &self.history,
+                self.kotlin_bridge.as_ref(),
+            ) {
                 watchers.push((r, w));
             }
         }
@@ -912,7 +945,9 @@ fn content_root_watcher(
     index: &Arc<ProjectIndex>,
     documents: &Arc<Documents>,
     history: &Arc<LocalHistory>,
+    kotlin_bridge: Option<&Arc<crate::kotlin_bridge::KotlinBridge>>,
 ) -> Option<Watcher> {
+    let kotlin_bridge = kotlin_bridge.cloned();
     let (index, documents, history) = (index.clone(), documents.clone(), history.clone());
     Watcher::start(
         dir,
@@ -921,6 +956,9 @@ fn content_root_watcher(
         Box::new(move |batch| {
             let changed: Vec<PathBuf> = batch.created.iter().chain(&batch.modified).cloned().collect();
             index.update(&changed, &batch.removed);
+            if let Some(bridge) = &kotlin_bridge {
+                bridge.files_changed(changed.iter().chain(&batch.removed));
+            }
             documents.on_disk_changed(&changed);
             record_external_changes(&history, &changed, &batch.removed);
         }),
diff --git a/crates/ide-host/src/rpc.rs b/crates/ide-host/src/rpc.rs
index e34db1e4a..78605b1e0 100644
--- a/crates/ide-host/src/rpc.rs
+++ b/crates/ide-host/src/rpc.rs
@@ -179,6 +179,7 @@ impl Dispatcher {
         })
         .add("cancel_task", |c| async move { Ok(ide_core::task::cancel(c.arg::<TaskId>("id")?)) })
         .add("fs_read_dir", |c| async move { ops::fs::read_dir(&c.host, &c.window, c.arg("path")?) })
+        .add("fs_entry_kind", |c| async move { ops::fs::entry_kind(&c.host, c.arg("path")?).await })
         .add("fs_create_file", |c| async move { ops::fs::create_file(&c.host, &c.window, c.arg("path")?) })
         .add("fs_create_file_bytes", |c| async move {
             ops::fs::create_file_bytes(&c.host, c.arg("path")?, c.arg("data")?).await
@@ -190,6 +191,28 @@ impl Dispatcher {
         })
         .add("fs_delete", |c| async move { ops::fs::delete(&c.host, &c.window, c.arg("path")?).await })
         .add("fs_copy", |c| async move { ops::fs::copy(&c.host, c.arg("from")?, c.arg("to")?).await })
+        .add("fs_copy_merge", |c| async move {
+            ops::fs::copy_merge(
+                &c.host,
+                &c.window,
+                c.arg("sourceRoot")?,
+                c.arg("destinationRoot")?,
+                c.arg("path")?,
+                c.arg("overwrite")?,
+            )
+            .await
+        })
+        .add("fs_compare_directories", |c| async move {
+            ops::fs::compare_directories(
+                &c.host,
+                &c.window,
+                c.arg("left")?,
+                c.arg("right")?,
+                c.arg("request")?,
+                c.sender("onProgress")?,
+            )
+            .await
+        })
         .add("fs_read_text", |c| async move { ops::fs::read_text(&c.host, &c.window, c.arg("path")?).await })
         .add("doc_open", |c| async move { ops::doc::open(&c.host, &c.window, c.arg("path")?).await })
         .add("doc_close", |c| async move { ops::doc::close(&c.host, &c.window, c.arg("doc")?) })
diff --git a/crates/ide-host/src/trust.rs b/crates/ide-host/src/trust.rs
index 9e1bfb826..b829bd636 100644
--- a/crates/ide-host/src/trust.rs
+++ b/crates/ide-host/src/trust.rs
@@ -106,6 +106,9 @@ impl crate::Host {
             if previous == trusted {
                 continue;
             }
+            if let Some(bridge) = &project.kotlin_bridge {
+                bridge.schedule();
+            }
             if !trusted {
                 project.lsp.set_execution_allowed(false);
             }
@@ -175,6 +178,30 @@ pub fn restricted_command_allowed(cmd: &str) -> bool {
     matches!(
         cmd,
         "app_info"
+            | "app_build_info"
+            | "app_log_location"
+            | "app_check_update"
+            | "app_startup_update_check"
+            | "app_install_update"
+            | "caches_schedule_invalidation"
+            | "clear_caches"
+            | "clipboard_file_list"
+            | "clipboard_has_files"
+            | "clipboard_set_file_list"
+            | "jdk_download_vendors"
+            | "jdk_download_releases"
+            | "jdk_download_location"
+            | "jdk_download"
+            | "run_system_env"
+            | "run_gradle_jvm_args_script"
+            | "proxy_check_connection"
+            | "docker_settings"
+            | "docker_save_settings"
+            | "docker_set_registry_password"
+            | "docker_run_env"
+            | "db_console_path"
+            | "db_export_file"
+            | "vcs_write_patch"
             | "app_metrics"
             | "app_quit"
             | "app_cancel_quit"
@@ -235,6 +262,7 @@ pub fn restricted_command_allowed(cmd: &str) -> bool {
             | "agent_registry_remove"
             | "coverage_import"
             | "system_font_families"
+            | "user_font_data"
             | "plugin_subscribe"
             | "plugin_list"
             | "plugin_set_active_file"
diff --git a/crates/ide-host/tests/properties.rs b/crates/ide-host/tests/properties.rs
index 097d92a63..dce783dd4 100644
--- a/crates/ide-host/tests/properties.rs
+++ b/crates/ide-host/tests/properties.rs
@@ -104,7 +104,7 @@ async fn properties_search_git_and_document_coordinates_agree() {
         "main",
         opened.id,
         opened.version,
-        ChangeSet { changes: vec![TextChange { from: 10, to: 16, insert: "世界".into() }] },
+        ChangeSet { changes: vec![TextChange { from: 10, to: 16, insert: r"\u4E16\u754C".into() }] },
     )
     .unwrap();
     let hunks = vcs::vcs_line_hunks(&host, "main", path.clone()).await.unwrap();
@@ -129,7 +129,7 @@ async fn properties_search_git_and_document_coordinates_agree() {
     assert!(project.documents.snapshot(opened.id).unwrap().version > snap.version);
     assert!(vcs::vcs_line_hunks(&host, "main", path.clone()).await.unwrap().is_empty());
     // Partial commits identify hunks in displayed line coordinates as well.
-    let partial_text = displayed.replace("target", "世界").replace("logical", "changed");
+    let partial_text = displayed.replace("target", r"\u4E16\u754C").replace("logical", "changed");
     project.documents.replace_all(opened.id, &partial_text).unwrap();
     doc::save(&host, "main", opened.id).await.unwrap();
     let hunks = ide_vcs::diff_hunks(displayed, &partial_text);
@@ -169,7 +169,7 @@ async fn properties_search_git_and_document_coordinates_agree() {
         "main",
         RequestId(520),
         query,
-        "世界".into(),
+        r"\u4E16\u754C".into(),
         false,
         vec![ide_search::ReplaceTarget {
             path: closed_path.clone().into(),
@@ -181,5 +181,6 @@ async fn properties_search_git_and_document_coordinates_agree() {
     .unwrap();
     assert_eq!(std::fs::read_to_string(&closed_path).unwrap(), r"value=\u4F60\u597D\uD83D\uDE00\u4E16\u754C");
     assert!(project.documents.by_path(&closed_path).is_none());
+    assert_eq!(project.text_of(&closed_path).unwrap(), "value=你好😀世界");
     host.close_project("main");
 }
diff --git a/crates/ide-host/tests/rpc.rs b/crates/ide-host/tests/rpc.rs
index d16f408fc..58e4ede39 100644
--- a/crates/ide-host/tests/rpc.rs
+++ b/crates/ide-host/tests/rpc.rs
@@ -94,6 +94,39 @@ async fn serves_projects_files_documents_search_and_runs() {
     let entries = invoke(&peer, "fs_read_dir", json!({ "path": project })).await.unwrap();
     assert!(entries.as_array().unwrap().iter().any(|e| e["name"] == "src"), "{entries}");
 
+    // Directory comparisons, streamed progress and confirmed copies share the remote filesystem.
+    let left = project.join("compare-left");
+    let right = project.join("compare-right");
+    std::fs::create_dir_all(&left).unwrap();
+    std::fs::create_dir_all(&right).unwrap();
+    std::fs::write(left.join("中文.bin"), [0, 255, 1]).unwrap();
+    std::fs::write(right.join("中文.bin"), [0, 254, 1]).unwrap();
+    assert_eq!(invoke(&peer, "fs_entry_kind", json!({"path": left})).await.unwrap(), "dir");
+    assert_eq!(invoke(&peer, "fs_entry_kind", json!({"path": left.join("中文.bin")})).await.unwrap(), "file");
+    let compare_args =
+        |request| json!({"left": left, "right": right, "request": request, "onProgress": {"$channel": 520}});
+    let rows = invoke(&peer, "fs_compare_directories", compare_args(520)).await.unwrap();
+    assert_eq!(rows[0]["status"], "different");
+    assert!(client.channels.lock().iter().any(|c| c.id == 520 && c.data["compared"] == 1));
+    let copy_args =
+        |overwrite| json!({"sourceRoot": left, "destinationRoot": right, "path": "中文.bin", "overwrite": overwrite});
+    let error = invoke(&peer, "fs_copy_merge", copy_args(false)).await.unwrap_err();
+    assert_eq!(error.kind, ide_core::error::ErrorKind::AlreadyExists);
+    invoke(&peer, "fs_copy_merge", copy_args(true)).await.unwrap();
+    let rows = invoke(&peer, "fs_compare_directories", compare_args(521)).await.unwrap();
+    assert_eq!(rows[0]["status"], "equal");
+    invoke(&peer, "cancel_request", json!({"id": 522})).await.unwrap();
+    let error = invoke(&peer, "fs_compare_directories", compare_args(522)).await.unwrap_err();
+    assert_eq!(error.kind, ide_core::error::ErrorKind::Cancelled);
+    let error = invoke(
+        &peer,
+        "fs_copy_merge",
+        json!({"sourceRoot": left, "destinationRoot": right, "path": "../escape", "overwrite": true}),
+    )
+    .await
+    .unwrap_err();
+    assert_eq!(error.kind, ide_core::error::ErrorKind::InvalidInput);
+
     // JVM icons use the same read-only protocol as local windows.
     let java = project.join("src/Foo.java");
     let kotlin = project.join("src/Singleton.kt");
diff --git a/crates/ide-host/tests/terminal_activation.rs b/crates/ide-host/tests/terminal_activation.rs
new file mode 100644
index 000000000..9561a23eb
--- /dev/null
+++ b/crates/ide-host/tests/terminal_activation.rs
@@ -0,0 +1,62 @@
+//! Own test process: the inherited shell deliberately differs from the login shell.
+#![cfg(unix)]
+
+use ide_core::NullSink;
+use ide_host::{Host, HostConfig, ops};
+use std::sync::Arc;
+use std::time::{Duration, Instant};
+
+#[test]
+fn terminal_activation_uses_the_resolved_default_shell() {
+    // SAFETY: no runtime or worker threads have been started.
+    unsafe { std::env::set_var("SHELL", "/not-the-terminal/docker") };
+    let tmp = tempfile::tempdir().unwrap();
+    let root = dunce::canonicalize(tmp.path()).unwrap().join("project");
+    let bin = root.join(".venv/bin");
+    std::fs::create_dir_all(&bin).unwrap();
+    std::fs::write(root.join(".venv/pyvenv.cfg"), "home = /usr/bin\n").unwrap();
+    std::fs::write(bin.join("python"), "").unwrap();
+    for script in ["activate", "activate.fish", "activate.csh", "activate.nu", "Activate.ps1"] {
+        std::fs::write(bin.join(script), "echo activated > activation.marker\n").unwrap();
+    }
+    let runtime = tokio::runtime::Builder::new_multi_thread().worker_threads(2).enable_all().build().unwrap();
+    runtime.block_on(async {
+        let host = Arc::new(Host::new(HostConfig {
+            config_dir: tmp.path().join("config"),
+            data_dir: tmp.path().join("data"),
+            languages: Arc::new(ide_language::LanguageRegistry::load(None).unwrap()),
+            syntax: Arc::default(),
+            sink_for: Box::new(|_| Arc::new(NullSink)),
+            owner: |w| w,
+            runtime: tokio::runtime::Handle::current(),
+            project_environment: false,
+        }));
+        host.trust.decide(&root, true, false).unwrap();
+        host.open_project("main", &root).unwrap();
+        for shell in [None, Some("".to_owned()), Some(" \t ".to_owned())] {
+            let terminal = ops::term::spawn(
+                &host,
+                "main",
+                ide_terminal::TerminalOptions {
+                    cwd: root.clone().into(),
+                    shell,
+                    args: vec![],
+                    env: Default::default(),
+                    cols: 80,
+                    rows: 24,
+                    shell_integration: false,
+                },
+                Arc::new(|_| {}),
+            )
+            .unwrap();
+            let deadline = Instant::now() + Duration::from_secs(10);
+            while !std::fs::read_to_string(root.join("activation.marker")).is_ok_and(|s| s.trim() == "activated") {
+                assert!(Instant::now() < deadline, "default terminal shell must run the activation script");
+                tokio::time::sleep(Duration::from_millis(20)).await;
+            }
+            host.terminals.kill(terminal.id).unwrap();
+            std::fs::remove_file(root.join("activation.marker")).unwrap();
+        }
+        host.shutdown().await;
+    });
+}
diff --git a/crates/ide-host/tests/trust.rs b/crates/ide-host/tests/trust.rs
index bf6a0a057..4a1d0250a 100644
--- a/crates/ide-host/tests/trust.rs
+++ b/crates/ide-host/tests/trust.rs
@@ -20,6 +20,94 @@ fn host(base: &Path, environment: bool) -> Arc<Host> {
     }))
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn application_commands_work_in_restricted_projects_and_without_a_project() {
+    let tmp = tempfile::tempdir().unwrap();
+    let root = tmp.path().join("project");
+    std::fs::create_dir(&root).unwrap();
+    let host = host(&tmp.path().join("app"), false);
+    assert!(host.project("welcome").is_err());
+    assert!(ide_host::ops::project::roots(&host, "welcome").is_err());
+    assert!(!host.open_project("main", &root).unwrap().is_trusted());
+    for command in [
+        "app_info",
+        "app_build_info",
+        "app_log_location",
+        "app_check_update",
+        "app_startup_update_check",
+        "app_install_update",
+        "caches_schedule_invalidation",
+        "clear_caches",
+        "clipboard_file_list",
+        "clipboard_has_files",
+        "clipboard_set_file_list",
+        "jdk_download_vendors",
+        "jdk_download_releases",
+        "jdk_download_location",
+        "jdk_download",
+        "run_system_env",
+        "run_gradle_jvm_args_script",
+        "proxy_check_connection",
+        "docker_settings",
+        "docker_save_settings",
+        "docker_set_registry_password",
+        "docker_run_env",
+        "db_console_path",
+        "db_export_file",
+        "vcs_write_patch",
+    ] {
+        assert!(ide_host::trust::restricted_command_allowed(command), "{command}");
+        for window in ["main", "welcome"] {
+            assert!(host.authorize_command(window, command).is_ok(), "{window}: {command}");
+        }
+    }
+    for command in [
+        "run_start",
+        "build_sync",
+        "debug_start",
+        "sdk_detect",
+        "tools_list",
+        "tools_install",
+        "tools_uninstall",
+        "plugin_install_dir",
+        "plugin_reload",
+        "vcs_git_version",
+        "docker_compose_op",
+        "db_execute",
+        "unknown_command",
+    ] {
+        assert!(!ide_host::trust::restricted_command_allowed(command), "{command}");
+        for window in ["main", "welcome"] {
+            assert!(host.authorize_command(window, command).is_err(), "{window}: {command}");
+        }
+    }
+    // These requests validate the vendor before any network access, independently of project trust.
+    for window in ["main", "welcome"] {
+        let error = ide_host::ops::tools::jdk_download_releases(
+            &host,
+            window,
+            "unknown-vendor".into(),
+            ide_core::RequestId(901),
+        )
+        .await
+        .unwrap_err();
+        assert_eq!(error.kind, ide_core::error::ErrorKind::InvalidInput);
+        let error = ide_host::ops::tools::jdk_download(
+            &host,
+            window,
+            "unknown-vendor".into(),
+            25,
+            None,
+            ide_core::RequestId(902),
+            ide_host::ops::Channel::new(|_| {}),
+        )
+        .await
+        .unwrap_err();
+        assert_eq!(error.kind, ide_core::error::ErrorKind::InvalidInput);
+    }
+    host.shutdown().await;
+}
+
 #[test]
 fn persists_user_decisions_locations_revocation_and_one_time_migration() {
     let tmp = tempfile::tempdir().unwrap();
diff --git a/crates/ide-language/src/lib.rs b/crates/ide-language/src/lib.rs
index fc935338f..a42587cc8 100644
--- a/crates/ide-language/src/lib.rs
+++ b/crates/ide-language/src/lib.rs
@@ -53,6 +53,19 @@ pub struct LanguageConfig {
     pub language_servers: Vec<LanguageServerConfig>,
     #[serde(default)]
     pub debugger: Option<DebuggerConfig>,
+    /// External formatter used when no language server can format, or selected in settings.
+    #[serde(default)]
+    pub formatter: Option<FormatterConfig>,
+}
+
+/// An external formatting tool and its language-specific parser.
+#[derive(Clone, Debug, Serialize, Deserialize)]
+#[serde(rename_all = "kebab-case")]
+pub struct FormatterConfig {
+    pub tool: String,
+    pub parser: String,
+    #[serde(default)]
+    pub range: bool,
 }
 
 /// A CodeMirror mode for the files of a framework's projects.
diff --git a/crates/ide-lsp/src/jdtls.rs b/crates/ide-lsp/src/jdtls.rs
index 6b47e143c..f2b79e0c1 100644
--- a/crates/ide-lsp/src/jdtls.rs
+++ b/crates/ide-lsp/src/jdtls.rs
@@ -189,6 +189,24 @@ pub struct JavaCompileError {
     pub message: String,
 }
 
+/// Holds off JDT writers while an external compiler builds and snapshots launch outputs.
+/// Restores current settings even when preparation fails or is cancelled.
+pub struct JavaExternalBuild {
+    server: Arc<Server>,
+    run: Running,
+    _lock: tokio::sync::OwnedMutexGuard<()>,
+}
+
+impl Drop for JavaExternalBuild {
+    fn drop(&mut self) {
+        self.server.java_autobuild_suspended.store(false, std::sync::atomic::Ordering::SeqCst);
+        let settings = crate::handler::all_settings(&self.server.effective_config());
+        if let Err(e) = self.run.peer.notify("workspace/didChangeConfiguration", json!({ "settings": settings })) {
+            tracing::debug!("jdtls: restoring autobuild: {e}");
+        }
+    }
+}
+
 /// Error diagnostics sorted by file and position, capped at `limit`, and their total.
 pub fn compile_errors(
     diagnostics: Vec<(PathBuf, lsp_types::Diagnostic)>,
@@ -378,7 +396,8 @@ impl LspManager {
         self.jdtls_command_cancellable(path, command, arguments, &CancellationToken::new()).await
     }
 
-    async fn jdtls_command_cancellable(
+    /// Cancellable delegate commands for project-owned background services.
+    pub async fn jdtls_command_cancellable(
         &self,
         path: &Path,
         command: &str,
@@ -433,9 +452,28 @@ impl LspManager {
             .map_err(|e| crate::rpc_err(&server.name, "java/projectConfigurationsUpdate", e))
     }
 
+    /// Pause autobuild before resolving the launch classpath. That query takes the
+    /// Java project's workspace scheduling rule, draining the interrupted autobuild.
+    /// Keep this guard until Maven outputs have been copied out of JDT's reach.
+    pub async fn java_external_build(&self, path: &Path, cancel: &CancellationToken) -> IdeResult<JavaExternalBuild> {
+        let (server, run) = self.jdtls(path, cancel).await?;
+        let lock = cancellable_wait(cancel, server.java_build_lock.clone().lock_owned()).await?;
+        server.java_autobuild_suspended.store(true, std::sync::atomic::Ordering::SeqCst);
+        let guard = JavaExternalBuild { server, run, _lock: lock };
+        let settings = crate::handler::all_settings(&guard.server.effective_config());
+        guard
+            .run
+            .peer
+            .notify("workspace/didChangeConfiguration", json!({ "settings": settings }))
+            .map_err(|e| crate::rpc_err(SERVER, "workspace/didChangeConfiguration", e))?;
+        Ok(guard)
+    }
+
     /// Incremental build of the jdtls workspace (`java/buildWorkspace`), so
     /// class files are up to date before a launch.
     pub async fn java_build(&self, path: &Path, cancel: &CancellationToken) -> IdeResult<JavaBuildStatus> {
+        let (server, _) = self.jdtls(path, cancel).await?;
+        let _lock = cancellable_wait(cancel, server.java_build_lock.lock()).await?;
         let mut v = self.jdtls_request(path, "java/buildWorkspace", json!(false), BUILD_TIMEOUT, cancel).await?;
         // The first build can finish the Maven import before ServiceReady is handled.
         let (server, run) = self.jdtls(path, cancel).await?;
@@ -532,6 +570,59 @@ impl LspManager {
         collect()
     }
 
+    /// Resolve a disk/archive class to project source or the server's binary document.
+    /// Archive URIs must come from JDT's Java model: fabricated handles cannot map debug lines.
+    pub async fn java_class_file(&self, path: &Path, archive: Option<(PathBuf, String)>) -> IdeResult<String> {
+        let cancel = CancellationToken::new();
+        self.jdtls(&self.project_root, &cancel).await?;
+        if let Some((jar, entry)) = archive {
+            let entry = entry
+                .strip_prefix("META-INF/versions/")
+                .and_then(|s| s.split_once('/').map(|(_, s)| s))
+                .unwrap_or(&entry);
+            let class = entry.strip_suffix(".class").ok_or_else(|| IdeError::not_found("expected a class file"))?;
+            let outer = class.split('$').next().unwrap_or(class);
+            let (package, name) = outer.rsplit_once('/').unwrap_or(("", outer));
+            let query = outer.replace('/', ".");
+            let symbols = self.workspace_symbols(&query, cancel).await?;
+            let package = package.replace('/', ".");
+            let name = name.to_owned();
+            let outer = outer.to_owned();
+            return tokio::task::spawn_blocking(move || {
+                symbols
+                    .into_iter()
+                    .filter_map(|s| s.location.uri)
+                    .find(|uri| crate::virtual_doc::matches_class(uri, &jar, &package, &name))
+                    .ok_or_else(|| {
+                        IdeError::not_found(format!("jdtls could not resolve {} in {}", outer, jar.display()))
+                    })
+            })
+            .await
+            .map_err(|e| IdeError::internal(e.to_string()))?;
+        }
+        let uri = crate::uri::path_to_uri_string(path);
+        // classFileContents accepts file URIs, but java-debug's line mapping only accepts JDT handles.
+        let doc = self.virtual_document(&uri).await?;
+        let name = path.file_stem().and_then(|s| s.to_str()).unwrap_or("").split('$').next().unwrap_or("");
+        let package = doc
+            .text
+            .lines()
+            .find_map(|l| l.trim().strip_prefix("package ").and_then(|p| p.strip_suffix(';')))
+            .unwrap_or("");
+        let relative = PathBuf::from(package.replace('.', "/")).join(format!("{name}.java"));
+        let key = "org.eclipse.jdt.ls.core.sourcePaths";
+        let settings = self
+            .jdtls_project_command(path, "java.project.getSettings", vec![json!(uri), json!([key])], &cancel)
+            .await?;
+        let roots: Vec<PathBuf> =
+            settings[key].as_array().into_iter().flatten().filter_map(Value::as_str).map(PathBuf::from).collect();
+        let source =
+            tokio::task::spawn_blocking(move || roots.into_iter().map(|r| r.join(&relative)).find(|p| p.is_file()))
+                .await
+                .map_err(|e| IdeError::internal(e.to_string()))?;
+        Ok(source.map(|s| s.to_string_lossy().into_owned()).unwrap_or(uri))
+    }
+
     /// Starts (or reuses) java-debug's DAP server inside jdtls and returns its port.
     pub async fn java_debug_server(&self, path: &Path) -> IdeResult<u16> {
         let v = self.jdtls_command(path, "vscode.java.startDebugSession", Vec::new()).await.map_err(|e| {
@@ -542,7 +633,7 @@ impl LspManager {
             }
         })?;
         // Hot code replace after each (auto-)build; errors only cost the feature.
-        let settings = json!({ "hotCodeReplace": "auto", "showStaticVariables": false, "showQualifiedNames": false,
+        let settings = json!({ "debugSupportOnDecompiledSource": "on", "hotCodeReplace": "auto", "showStaticVariables": false, "showQualifiedNames": false,
             "showLogicalStructure": true, "showToString": true, "maxStringLength": 0,
             // java-debug NPEs on a missing level (java.util.logging names).
             "logLevel": "WARNING" });
@@ -574,6 +665,7 @@ mod tests {
         assert_eq!(settings["java"]["project"]["sourcePaths"], json!(["src/main/java", "tests"]));
         assert_eq!(settings["java"]["project"]["referencedLibraries"], json!(["lib/**/*.jar"]));
         assert_eq!(settings["java"]["autobuild"]["enabled"], true);
+        assert_eq!(settings["java"]["contentProvider"]["preferred"], "fernflowerContentProvider");
         assert!(settings.get("bundles").is_none());
         assert!(settings.get("settings").is_none(), "didChangeConfiguration takes java settings directly");
     }
diff --git a/crates/ide-lsp/src/lib.rs b/crates/ide-lsp/src/lib.rs
index 6d44afeb9..521451845 100644
--- a/crates/ide-lsp/src/lib.rs
+++ b/crates/ide-lsp/src/lib.rs
@@ -1886,6 +1886,12 @@ impl LspManager {
         }
     }
 
+    /// Checks initialized capabilities, including dynamic registrations, before choosing a formatter.
+    pub async fn can_format(&self, doc: DocId) -> IdeResult<bool> {
+        let snap = self.snapshot(doc)?;
+        Ok(!self.ready_targets(&snap.servers, |c| c.has("documentFormattingProvider")).await.is_empty())
+    }
+
     pub async fn format(&self, doc: DocId, range: Option<Range>, options: FormatOptions) -> IdeResult<Vec<TextEdit>> {
         let (method, cap, feature) = match range {
             None => ("textDocument/formatting", "documentFormattingProvider", "formatting"),
@@ -2166,6 +2172,7 @@ impl LspManager {
             return Ok(d.clone());
         }
         let scheme = virtual_doc::scheme(uri).to_owned();
+        let class_file = scheme == "jdt" || (scheme == "file" && uri.ends_with(".class"));
         let origin = self.origin_server(uri);
         let mut servers: Vec<Arc<Server>> = origin.iter().cloned().collect();
         servers.extend(self.servers.lock().iter().filter(|s| Some(s.id) != origin.as_ref().map(|o| o.id)).cloned());
@@ -2174,7 +2181,7 @@ impl LspManager {
         for t in &targets {
             let languages = t.server.languages();
             let serves_scheme = t.caps().content_schemes().contains(&scheme);
-            let result: IdeResult<Option<String>> = if serves_scheme {
+            let result: IdeResult<Option<String>> = if serves_scheme && !class_file {
                 self.call::<_, Option<Value>>(
                     t,
                     "workspace/textDocumentContent",
@@ -2184,7 +2191,7 @@ impl LspManager {
                 )
                 .await
                 .map(|v| v.and_then(|v| v.get("text").and_then(Value::as_str).map(str::to_owned)))
-            } else if scheme == "jdt" && languages.iter().any(|l| l.as_str() == "java") {
+            } else if class_file && languages.iter().any(|l| l.as_str() == "java") {
                 self.call::<_, Option<String>>(t, "java/classFileContents", json!({ "uri": uri }), None, LONG_TIMEOUT)
                     .await
             } else {
diff --git a/crates/ide-lsp/src/server.rs b/crates/ide-lsp/src/server.rs
index 018c81ee0..81c21b021 100644
--- a/crates/ide-lsp/src/server.rs
+++ b/crates/ide-lsp/src/server.rs
@@ -99,6 +99,8 @@ pub struct Server {
     /// Woken when the last `$/progress` task ends.
     idle_notify: Notify,
     transient: Mutex<HashMap<PathBuf, Transient>>,
+    pub java_build_lock: Arc<tokio::sync::Mutex<()>>,
+    pub java_autobuild_suspended: std::sync::atomic::AtomicBool,
     pub external_project: tokio::sync::Mutex<crate::external_project::State>,
     pub external_diagnostics: std::sync::atomic::AtomicBool,
     pub external_refresh_queued: std::sync::atomic::AtomicBool,
@@ -126,6 +128,8 @@ impl Server {
             published_notify: Notify::new(),
             idle_notify: Notify::new(),
             transient: Mutex::new(HashMap::new()),
+            java_build_lock: Arc::new(tokio::sync::Mutex::new(())),
+            java_autobuild_suspended: std::sync::atomic::AtomicBool::new(false),
             external_project: tokio::sync::Mutex::new(Default::default()),
             external_diagnostics: std::sync::atomic::AtomicBool::new(false),
             external_refresh_queued: std::sync::atomic::AtomicBool::new(false),
@@ -134,7 +138,13 @@ impl Server {
 
     /// Configuration of the current (or last) instance; the base config before the first launch.
     pub fn effective_config(&self) -> LanguageServerConfig {
-        self.effective.lock().clone().unwrap_or_else(|| self.config.clone())
+        let mut config = self.effective.lock().clone().unwrap_or_else(|| self.config.clone());
+        if self.java_autobuild_suspended.load(std::sync::atomic::Ordering::SeqCst) {
+            let mut settings = crate::handler::all_settings(&config);
+            settings["java"]["autobuild"]["enabled"] = serde_json::json!(false);
+            config.settings = Some(settings);
+        }
+        config
     }
 
     pub fn set_effective_config(&self, config: LanguageServerConfig) {
@@ -553,6 +563,19 @@ mod tests {
         assert_eq!(s.record_crash(), Some(Duration::from_millis(500)));
     }
 
+    #[test]
+    fn external_build_suspends_only_the_effective_autobuild_setting() {
+        let mut config: LanguageServerConfig = toml::from_str("name = \"jdtls\"\ncommand = \"jdtls\"").unwrap();
+        config.settings = Some(serde_json::json!({"java": {"autobuild": {"enabled": true}, "other": "kept"}}));
+        let server = Server::new(config.clone(), PathBuf::from("/p"), LanguageId::new("java"));
+        server.java_autobuild_suspended.store(true, std::sync::atomic::Ordering::SeqCst);
+        let settings = crate::handler::all_settings(&server.effective_config());
+        assert_eq!(settings["java"]["autobuild"]["enabled"], false);
+        assert_eq!(settings["java"]["other"], "kept");
+        server.java_autobuild_suspended.store(false, std::sync::atomic::Ordering::SeqCst);
+        assert_eq!(server.effective_config(), config);
+    }
+
     #[tokio::test(flavor = "multi_thread")]
     async fn a_failed_start_reports_its_status_before_waiters_wake() {
         // The race behind "jdtls is not ready (Starting)": a request woken by the
diff --git a/crates/ide-lsp/src/types.rs b/crates/ide-lsp/src/types.rs
index 45be5d0c3..050d493d1 100644
--- a/crates/ide-lsp/src/types.rs
+++ b/crates/ide-lsp/src/types.rs
@@ -219,6 +219,9 @@ pub struct CodeActionQuery {
 pub struct FormatOptions {
     pub tab_size: u32,
     pub insert_spaces: bool,
+    #[serde(default)]
+    #[specta(optional)]
+    pub on_save: bool,
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize, Type)]
@@ -335,7 +338,7 @@ pub struct VirtualDocument {
     pub title: String,
     /// Origin shown in the tooltip / banner, e.g. the jar path.
     pub description: Option<String>,
-    /// Generated by a decompiler / disassembler rather than real sources.
+    /// Generated Java from a decompiler, rather than real source or a disassembler stub.
     pub decompiled: bool,
 }
 
diff --git a/crates/ide-lsp/src/virtual_doc.rs b/crates/ide-lsp/src/virtual_doc.rs
index 71394d7a1..110b206fd 100644
--- a/crates/ide-lsp/src/virtual_doc.rs
+++ b/crates/ide-lsp/src/virtual_doc.rs
@@ -1,21 +1,29 @@
 //! Virtual documents: read-only contents a language server provides for a
-//! non-`file:` URI (library classes from `jdt://`, `workspace/textDocumentContent`).
+//! URI (library classes from `jdt://`, disk classes from `file://`, or
+//! `workspace/textDocumentContent`).
 
 use percent_encoding::percent_decode_str;
 
-/// Markers decompilers / disassemblers put at the top of generated code.
-const GENERATED_MARKERS: [&str; 5] = [
-    "generated by the fernflower decompiler",
-    "failed to get sources",
-    "decompiled with cfr",
-    "decompiled with procyon",
-    "generated by the disassembler",
-];
-
-/// Whether `text` is decompiled / disassembled code rather than real source.
+/// Recognize decompiler headers, without treating disassembler stubs as Java source.
 pub fn is_decompiled(text: &str) -> bool {
-    let head: String = text.chars().take(600).collect::<String>().to_ascii_lowercase();
-    GENERATED_MARKERS.iter().any(|m| head.contains(m))
+    let head: String = text.chars().take(600).collect();
+    head.lines()
+        .take(12)
+        .take_while(|line| {
+            let line = line.trim();
+            line.is_empty() || line.starts_with("//") || line.starts_with("/*") || line.starts_with('*')
+        })
+        .any(|line| {
+            let line = line.trim().trim_start_matches('/').trim_start_matches('*').trim().to_ascii_lowercase();
+            [
+                "source code is unavailable, and was generated by the fernflower decompiler.",
+                "source code is decompiled from a .class file using fernflower decompiler",
+                "decompiled with cfr",
+                "decompiled with procyon",
+            ]
+            .iter()
+            .any(|marker| line.starts_with(marker))
+        })
 }
 
 /// `scheme` of a URI (`jdt` for `jdt://…`).
@@ -34,7 +42,16 @@ fn segments(uri: &str) -> Vec<String> {
 /// Editor tab title: the last path segment; a class file whose real source
 /// was found is shown as `.java` (IDEA: `String.java` vs `String.class`).
 pub fn title(uri: &str, decompiled: bool) -> String {
-    let name = segments(uri).pop().unwrap_or_else(|| uri.to_owned());
+    let mut name = segments(uri).pop().unwrap_or_else(|| uri.to_owned());
+    // Recent jdtls versions use a .java path even for decompiled class handles.
+    if decompiled
+        && scheme(uri) == "jdt"
+        && name.ends_with(".java")
+        && uri.split_once('?').is_some_and(|(_, q)| percent_decode_str(q).decode_utf8_lossy().contains(".class"))
+    {
+        name.truncate(name.len() - 5);
+        name.push_str(".class");
+    }
     match name.strip_suffix(".class") {
         Some(stem) if !decompiled && scheme(uri) == "jdt" => format!("{stem}.java"),
         _ => name,
@@ -68,6 +85,19 @@ pub fn description(uri: &str) -> Option<String> {
     }
 }
 
+/// Check both the package and actual archive, so duplicate type names never pick another jar.
+pub(crate) fn matches_class(uri: &str, jar: &std::path::Path, package: &str, name: &str) -> bool {
+    let segs = segments(uri);
+    scheme(uri) == "jdt"
+        && (package.is_empty() && segs.len() == 3 || segs.get(2).is_some_and(|s| s == package))
+        && segs.last().is_some_and(|s| s == &format!("{name}.class") || s == &format!("{name}.java"))
+        && description(uri).is_some_and(|p| {
+            let path = std::path::Path::new(&p);
+            path == jar
+                || dunce::canonicalize(path).ok().zip(dunce::canonicalize(jar).ok()).is_some_and(|(a, b)| a == b)
+        })
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -84,6 +114,30 @@ mod tests {
 
     #[test]
     fn jdt_description() {
+        assert!(matches_class(
+            JDT,
+            std::path::Path::new("/Users/me/.m2/repository/spring-boot-4.1.1.jar"),
+            "org.springframework.boot",
+            "SpringApplication"
+        ));
+        assert!(!matches_class(
+            JDT,
+            std::path::Path::new("/elsewhere/spring-boot-4.1.1.jar"),
+            "org.springframework.boot",
+            "SpringApplication"
+        ));
+        assert!(!matches_class(
+            JDT,
+            std::path::Path::new("/Users/me/.m2/repository/spring-boot-4.1.1.jar"),
+            "other.package",
+            "SpringApplication"
+        ));
+        assert!(matches_class(
+            "jdt://contents/a.jar//C.java?=p/%5C/m2%5C/a.jar%3C%28C.class",
+            std::path::Path::new("/m2/a.jar"),
+            "",
+            "C"
+        ));
         assert_eq!(description(JDT).as_deref(), Some("/Users/me/.m2/repository/spring-boot-4.1.1.jar"));
         assert_eq!(
             description(
@@ -98,10 +152,18 @@ mod tests {
 
     #[test]
     fn detects_generated_code() {
+        assert!(is_decompiled(
+            "// Source code is decompiled from a .class file using FernFlower decompiler (from Intellij IDEA).\npackage a;"
+        ));
+        assert!(!is_decompiled("package a;\n// generated by the fernflower decompiler"));
+        assert!(!is_decompiled("// Documentation about code generated by the Fernflower decompiler.\npackage a;"));
+        let recent = "jdt://contents/a.jar/p/C.java?=p/a.jar%3Cp%28C.class";
+        assert_eq!(title(recent, true), "C.class");
+        assert_eq!(title(recent, false), "C.java");
         assert!(is_decompiled(
             "// Source code is unavailable, and was generated by the Fernflower decompiler.\npackage a;"
         ));
-        assert!(is_decompiled(
+        assert!(!is_decompiled(
             "// Failed to get sources. Instead, stub sources have been generated by the disassembler."
         ));
         assert!(!is_decompiled("/*\n * Copyright 2012-2024 the original author or authors.\n */\npackage a;"));
diff --git a/crates/ide-lsp/tests/mock_server.rs b/crates/ide-lsp/tests/mock_server.rs
index e909af815..a636e5e4d 100644
--- a/crates/ide-lsp/tests/mock_server.rs
+++ b/crates/ide-lsp/tests/mock_server.rs
@@ -252,6 +252,7 @@ fn harness_configured(
         indent: None,
         ui_mode: None,
         framework_ui_modes: Vec::new(),
+        formatter: None,
         tree_sitter: None,
         language_servers: servers
             .iter()
@@ -1248,12 +1249,17 @@ async fn navigation_rename_format_and_decorations() {
     assert!(matches!(&edit.files[0], FileEdit::Edit { edits, .. } if edits.len() == 2));
     assert_eq!(s.requested("textDocument/rename")[0]["newName"], "bar");
 
+    assert!(h.mgr.can_format(doc).await.unwrap());
     s.respond("textDocument/formatting", json!([{ "range": r(0,10,0,11), "newText": "\n}" }]));
-    let edits = h.mgr.format(doc, None, FormatOptions { tab_size: 2, insert_spaces: true }).await.unwrap();
+    let edits =
+        h.mgr.format(doc, None, FormatOptions { tab_size: 2, insert_spaces: true, on_save: false }).await.unwrap();
     assert_eq!(edits[0].range, rng(0, 10, 0, 11));
     assert_eq!(s.requested("textDocument/formatting")[0]["options"], json!({ "tabSize": 2, "insertSpaces": true }));
     assert!(
-        h.mgr.format(doc, Some(rng(0, 0, 1, 0)), FormatOptions { tab_size: 2, insert_spaces: true }).await.is_err()
+        h.mgr
+            .format(doc, Some(rng(0, 0, 1, 0)), FormatOptions { tab_size: 2, insert_spaces: true, on_save: false })
+            .await
+            .is_err()
     );
 
     s.respond("textDocument/semanticTokens/full", json!({ "data": [0, 3, 3, 0, 1, 1, 0, 3, 0, 0] }));
@@ -1617,6 +1623,61 @@ async fn jdt_class_file_contents() {
     assert_eq!(vd.title, "Lib.class");
     assert_eq!(vd.language_id.as_str(), "java");
     assert_eq!(vd.description.as_deref(), Some("/m2/lib-1.0.jar"));
+    let source_uri = jdt.replace("Lib.class", "WithSources.class");
+    s.respond(
+        "java/classFileContents",
+        json!("/* Copyright library author */\npackage org.example;\npublic class WithSources {}"),
+    );
+    let source = h.mgr.virtual_document(&source_uri).await.unwrap();
+    assert!(!source.decompiled);
+    assert_eq!(source.title, "WithSources.java");
+}
+
+#[tokio::test(flavor = "multi_thread")]
+async fn class_file_opening_routes_sources_and_binary_documents() {
+    let mut caps = incremental_caps();
+    caps["workspaceSymbolProvider"] = json!(true);
+    let h = harness_for("java", "java", &[("jdtls", caps)], &[]);
+    h.open("App.java", "class App {}\n");
+    h.wait_status("jdtls", ServerStatus::Ready).await;
+    let s = h.launcher.state("jdtls");
+    let jdt = "jdt://contents/lib.jar/p/Outer.java?=demo/%5C/m2%5C/lib.jar%3Cp%28Outer.class";
+    s.respond("workspace/symbol", json!([
+        {"name":"Outer", "kind":5, "location":{"uri":jdt,"range":{"start":{"line":0,"character":0},"end":{"line":0,"character":0}}}}
+    ]));
+    let archive = Some((PathBuf::from("/m2/lib.jar"), "p/Outer$1.class".into()));
+    assert_eq!(h.mgr.java_class_file(Path::new("/m2/lib.jar!/p/Outer$1.class"), archive).await.unwrap(), jdt);
+    assert!(
+        h.mgr
+            .java_class_file(
+                Path::new("/other/lib.jar!/p/Outer.class"),
+                Some(("/other/lib.jar".into(), "p/Outer.class".into()))
+            )
+            .await
+            .is_err()
+    );
+
+    let sources = h.root.join("src/main/java");
+    std::fs::create_dir_all(sources.join("p")).unwrap();
+    let source = sources.join("p/Outer.java");
+    std::fs::write(&source, "package p; class Outer {} ").unwrap();
+    s.respond("java/classFileContents", json!("// Source code is decompiled from a .class file using FernFlower decompiler (from Intellij IDEA).\npackage p;\npublic class Outer {}"));
+    s.respond("workspace/executeCommand", json!({"org.eclipse.jdt.ls.core.sourcePaths":[sources]}));
+    for class in ["Outer", "Outer$Nested", "Outer$1"] {
+        let path = h.root.join(format!("target/classes/p/{class}.class"));
+        let resolved = h.mgr.java_class_file(&path, None).await.unwrap();
+        // Compare as paths: the manager joins the relative source path with std::path, so
+        // separators can differ from the literal "p/Outer.java" used to build `source` on Windows.
+        assert_eq!(Path::new(&resolved), source.as_path());
+    }
+    let path = h.root.join("build/classes/java/main/p/Missing.class");
+    let uri = uri_of(&path);
+    assert_eq!(h.mgr.java_class_file(&path, None).await.unwrap(), uri);
+    let vd = h.mgr.virtual_document(&uri).await.unwrap();
+    assert!(vd.decompiled);
+    assert_eq!(vd.language_id.as_str(), "java");
+    assert_eq!(vd.title, "Missing.class");
+    assert!(s.requested("java/classFileContents").iter().any(|p| p["uri"] == uri));
 }
 
 #[tokio::test(flavor = "multi_thread")]
@@ -2682,3 +2743,32 @@ async fn interactive_capability_is_scoped_to_gopls() {
     assert!(form.is_none());
     assert!(s.requested("command/resolve").is_empty());
 }
+
+#[tokio::test(flavor = "multi_thread")]
+async fn formatting_provider_selection_tracks_dynamic_registration() {
+    let h = harness(&[("mock", json!({ "textDocumentSync": 1, "documentRangeFormattingProvider": true }))]);
+    let (doc, _) = h.open("a.mk", "hello\n");
+    h.wait_status("mock", ServerStatus::Ready).await;
+    assert!(!h.mgr.can_format(doc).await.unwrap(), "a range provider alone cannot format the whole document");
+    let peer = h.launcher.state("mock").peer();
+    peer.request::<_, Value>(
+        "client/registerCapability",
+        json!({"registrations": [
+            {"id": "formatter", "method": "textDocument/formatting"}
+        ]}),
+        None,
+    )
+    .await
+    .unwrap();
+    assert!(h.mgr.can_format(doc).await.unwrap());
+    peer.request::<_, Value>(
+        "client/unregisterCapability",
+        json!({"unregisterations": [
+            {"id": "formatter", "method": "textDocument/formatting"}
+        ]}),
+        None,
+    )
+    .await
+    .unwrap();
+    assert!(!h.mgr.can_format(doc).await.unwrap());
+}
diff --git a/crates/ide-lsp/tests/real_servers.rs b/crates/ide-lsp/tests/real_servers.rs
index 13ab9667f..43c250a20 100644
--- a/crates/ide-lsp/tests/real_servers.rs
+++ b/crates/ide-lsp/tests/real_servers.rs
@@ -55,6 +55,7 @@ fn lang(id: &str, ext: &str, server: LanguageServerConfig) -> LanguageConfig {
         indent: None,
         ui_mode: None,
         framework_ui_modes: Vec::new(),
+        formatter: None,
         tree_sitter: None,
         language_servers: vec![server],
         debugger: None,
diff --git a/crates/ide-sdk/src/apply.rs b/crates/ide-sdk/src/apply.rs
index f093c8d4c..a397529c2 100644
--- a/crates/ide-sdk/src/apply.rs
+++ b/crates/ide-sdk/src/apply.rs
@@ -735,8 +735,8 @@ fn sh_quote(s: &str) -> String {
 }
 
 /// Command typed into a new terminal to activate the project virtualenv
-/// (PyCharm's Tools › Terminal › "Activate virtualenv"), for the given shell.
-pub fn terminal_activation(root: &Path, s: &Settings, shell: Option<&str>) -> Option<String> {
+/// (Tools › Terminal › "Activate virtualenv"). `shell` must be the resolved PTY shell.
+pub fn terminal_activation(root: &Path, s: &Settings, shell: &str) -> Option<String> {
     if !s.languages.python.activate_virtualenv {
         return None;
     }
@@ -744,12 +744,8 @@ pub fn terminal_activation(root: &Path, s: &Settings, shell: Option<&str>) -> Op
     if std::env::var_os("VIRTUAL_ENV").is_some_and(|v| Path::new(&v) == venv) {
         return None;
     }
-    let shell = shell
-        .map(str::to_owned)
-        .or_else(|| std::env::var("SHELL").ok())
-        .or_else(|| std::env::var("COMSPEC").ok())
-        .unwrap_or_default();
-    let name = Path::new(&shell).file_stem().map(|n| n.to_string_lossy().to_lowercase()).unwrap_or_default();
+    let name = shell.rsplit(['/', '\\']).next().unwrap_or(shell);
+    let name = Path::new(name).file_stem().map(|n| n.to_string_lossy().to_lowercase()).unwrap_or_default();
     let script = |file: &str| venv.join(bin_dir()).join(file);
     let line = match name.as_str() {
         "fish" => format!("source {}", sh_quote(&script("activate.fish").to_string_lossy())),
diff --git a/crates/ide-sdk/src/java.rs b/crates/ide-sdk/src/java.rs
index 755778568..9d104583a 100644
--- a/crates/ide-sdk/src/java.rs
+++ b/crates/ide-sdk/src/java.rs
@@ -717,6 +717,20 @@ mod tests {
         configure_jdtls(&mut plain, Path::new("/p"), Path::new("/data"), &[], None, None, JDTLS_MIN_JAVA, &[], None);
         let data = |c: &LanguageServerConfig| c.args[c.args.iter().position(|a| a == "-data").unwrap() + 1].clone();
         assert_ne!(data(&cfg), data(&plain), "a separate workspace, so everything is rebuilt with the agent");
+        let patched = Path::new("/managed/lombok-1.18.48-openidea.1.jar");
+        let mut fixed = jdtls();
+        configure_jdtls(
+            &mut fixed,
+            Path::new("/p"),
+            Path::new("/data"),
+            &[],
+            None,
+            None,
+            JDTLS_MIN_JAVA,
+            &[],
+            Some(patched),
+        );
+        assert_ne!(data(&cfg), data(&fixed), "the patch must rebuild classes compiled with the official agent");
         let before = cfg.clone();
         configure_jdtls(&mut cfg, Path::new("/p"), Path::new("/data"), &[], None, None, JDTLS_MIN_JAVA, &[], Some(jar));
         assert_eq!(cfg, before, "idempotent");
@@ -934,6 +948,49 @@ mod tests {
     }
 }
 
+/// The same jar supplies the JDT command and the private Maven output redirector.
+pub fn kotlin_bridge_bundle(data_dir: &Path) -> Option<PathBuf> {
+    let extension = data_dir.join("kotlin-bridge-1.0.0.jar");
+    let bytes = include_bytes!("../../../plugins/kotlin-bridge/openidea-kotlin-bridge.jar");
+    if std::fs::read(&extension).is_ok_and(|old| old == bytes) {
+        return Some(extension);
+    }
+    let temporary = data_dir.join(format!(
+        "kotlin-bridge-{}-{}.tmp",
+        std::process::id(),
+        std::time::SystemTime::now().duration_since(std::time::UNIX_EPOCH).ok()?.as_nanos()
+    ));
+    let result = std::fs::create_dir_all(data_dir)
+        .and_then(|_| std::fs::write(&temporary, bytes))
+        .and_then(|_| std::fs::rename(&temporary, &extension));
+    if let Err(error) = result {
+        let _ = std::fs::remove_file(temporary);
+        tracing::warn!("Kotlin bridge extension unavailable: {error}");
+        return std::fs::read(&extension).is_ok_and(|old| old == bytes).then_some(extension);
+    }
+    Some(extension)
+}
+
+#[cfg(test)]
+mod kotlin_bridge_bundle_tests {
+    #[test]
+    fn embeds_both_runtime_targets_and_repairs_a_damaged_installation() {
+        let directory = tempfile::tempdir().unwrap();
+        let path = super::kotlin_bridge_bundle(directory.path()).unwrap();
+        let expected = std::fs::read(&path).unwrap();
+        let mut archive = zip::ZipArchive::new(std::io::Cursor::new(&expected)).unwrap();
+        for (class, major) in [("KotlinLibraries", 65), ("IsolatedOutput", 52)] {
+            use std::io::Read;
+            let mut bytes = Vec::new();
+            archive.by_name(&format!("ai/openidea/kotlin/{class}.class")).unwrap().read_to_end(&mut bytes).unwrap();
+            assert_eq!(u16::from_be_bytes([bytes[6], bytes[7]]), major);
+        }
+        std::fs::write(&path, "incomplete").unwrap();
+        assert_eq!(super::kotlin_bridge_bundle(directory.path()), Some(path.clone()));
+        assert_eq!(std::fs::read(path).unwrap(), expected);
+    }
+}
+
 /// Installs the app-owned JDT LS command bundle, falling back to ordinary LSP on IO failure.
 pub fn usages_bundle(data_dir: &Path) -> Option<PathBuf> {
     let extension = data_dir.join("java-usages-1.1.1.jar");
diff --git a/crates/ide-sdk/src/libraries.rs b/crates/ide-sdk/src/libraries.rs
index 4c50b2f55..bdc450b7e 100644
--- a/crates/ide-sdk/src/libraries.rs
+++ b/crates/ide-sdk/src/libraries.rs
@@ -8,7 +8,7 @@
 //! result is cached until the manifests (or the relevant settings) change.
 //!
 //! Archives are listed as browsable roots (`<archive>!`, see `ide_vfs`): the
-//! JDK's `src.zip` and the Maven / Gradle dependency jars (sources jars preferred).
+//! JDK's `src.zip` and the Maven / Gradle dependency jars (source attachments resolved by JDT).
 
 use crate::exe;
 use crate::exec::{query, query_in, which};
@@ -248,7 +248,7 @@ fn gradle_user_home() -> Option<PathBuf> {
 }
 
 /// One `Maven: g:a:v` / `Gradle: g:a:v` group per dependency whose jar is in a
-/// local repository, its root being the jar (the `-sources.jar` when downloaded).
+/// local repository, its root being the binary jar so Java classes open through JDT's source provider.
 pub(crate) fn dependency_libraries(
     deps: &[BuildDependency],
     maven_repo: Option<&Path>,
@@ -286,7 +286,7 @@ pub(crate) fn maven_jar(repo: &Path, d: &BuildDependency) -> Option<PathBuf> {
         return None;
     }
     let dir = repo.join(d.group.replace('.', "/")).join(&d.artifact).join(&d.version);
-    ["-sources.jar", ".jar"]
+    [".jar", "-sources.jar"]
         .iter()
         .map(|suffix| dir.join(format!("{}-{}{suffix}", d.artifact, d.version)))
         .find(|p| p.is_file())
@@ -300,7 +300,7 @@ pub(crate) fn gradle_jar(home: &Path, d: &BuildDependency) -> Option<PathBuf> {
     let dir = home.join("caches/modules-2/files-2.1").join(&d.group).join(&d.artifact).join(&d.version);
     let mut hashes: Vec<PathBuf> = std::fs::read_dir(dir).ok()?.flatten().map(|e| e.path()).collect();
     hashes.sort();
-    ["-sources.jar", ".jar"].iter().find_map(|suffix| {
+    [".jar", "-sources.jar"].iter().find_map(|suffix| {
         let file = format!("{}-{}{suffix}", d.artifact, d.version);
         hashes.iter().map(|h| h.join(&file)).find(|p| p.is_file())
     })
diff --git a/crates/ide-sdk/src/lombok.rs b/crates/ide-sdk/src/lombok.rs
index f8958bc40..67c383385 100644
--- a/crates/ide-sdk/src/lombok.rs
+++ b/crates/ide-sdk/src/lombok.rs
@@ -1,6 +1,6 @@
 //! Lombok for jdtls: ECJ only generates Lombok members when the language
 //! server's JVM runs `-javaagent:lombok.jar`, so a project using Lombok gets the
-//! newest jar available, managed (installed by the IDE) or in the Maven / Gradle caches.
+//! app-provided jar, or falls back to the newest release in the Maven / Gradle caches.
 
 use crate::home_dir;
 use std::path::{Path, PathBuf};
@@ -18,7 +18,7 @@ pub enum LombokAgent {
     Missing,
     Found {
         jar: PathBuf,
-        /// `None` for the managed jar (the latest release when installed).
+        /// `None` for the app-provided jar (its version is shown by the tool registry).
         version: Option<String>,
     },
 }
@@ -64,7 +64,7 @@ pub fn agent_in_args<'a>(args: impl IntoIterator<Item = &'a str>) -> Option<Path
 }
 
 /// The Lombok agent for the project at `root`: the user's own (`own`, from the JVM
-/// options) wins, then `managed` (the IDE-installed jar, always attached: it is inert
+/// options) wins, then `managed` (the app-provided jar, always attached: it is inert
 /// without Lombok on the classpath), then, for a project using Lombok, the build caches
 /// (`maven_repo`, the configured Maven local repository, else the default one).
 pub fn lombok_agent(
@@ -499,6 +499,23 @@ mod tests {
         assert_eq!(managed.problem(), None);
     }
 
+    #[test]
+    fn the_patched_agent_wins_over_project_caches_but_respects_explicit_overrides() {
+        let tmp = tempfile::tempdir().unwrap();
+        fs::write(tmp.path().join("pom.xml"), LOMBOK_DEP).unwrap();
+        let repo = tmp.path().join("m2");
+        let cache = repo.join("org/projectlombok/lombok/1.18.48");
+        fs::create_dir_all(&cache).unwrap();
+        fs::write(cache.join("lombok-1.18.48.jar"), b"official agent").unwrap();
+        let patched = PathBuf::from("/managed/lombok-1.18.48-openidea.1.jar");
+        let selected = lombok_agent(tmp.path(), None, Some(patched.clone()), Some(repo.clone()));
+        assert_eq!(selected.jar(), Some(patched.as_path()));
+        assert_eq!(selected.problem(), None);
+        let own = PathBuf::from("/custom/lombok.jar");
+        let selected = lombok_agent(tmp.path(), Some(own.clone()), Some(patched), Some(repo));
+        assert_eq!(selected.jar(), Some(own.as_path()));
+    }
+
     #[test]
     fn picks_the_newest_cached_release() {
         let tmp = tempfile::tempdir().unwrap();
diff --git a/crates/ide-sdk/src/tests.rs b/crates/ide-sdk/src/tests.rs
index 1dcfee226..37adca8be 100644
--- a/crates/ide-sdk/src/tests.rs
+++ b/crates/ide-sdk/src/tests.rs
@@ -319,14 +319,40 @@ fn terminal_activation_for_project_venv() {
     }
     let tmp = tempfile::tempdir().unwrap();
     let mut s = Settings::default();
-    assert_eq!(terminal_activation(tmp.path(), &s, Some("/bin/zsh")), None);
+    assert_eq!(terminal_activation(tmp.path(), &s, "/bin/zsh"), None);
     fake_venv(tmp.path(), ".venv");
-    let line = terminal_activation(tmp.path(), &s, Some("/bin/zsh")).unwrap();
+    let line = terminal_activation(tmp.path(), &s, "/bin/zsh").unwrap();
     assert!(line.starts_with("source '") && line.ends_with("/activate'"), "{line}");
-    assert_eq!(terminal_activation(tmp.path(), &s, Some("/usr/bin/fish")), None, "no activate.fish");
-    assert_eq!(terminal_activation(tmp.path(), &s, Some("docker")), None, "not a shell");
+    assert_eq!(terminal_activation(tmp.path(), &s, "/usr/bin/fish"), None, "no activate.fish");
+    assert_eq!(terminal_activation(tmp.path(), &s, "docker"), None, "not a shell");
     s.languages.python.activate_virtualenv = false;
-    assert_eq!(terminal_activation(tmp.path(), &s, Some("/bin/zsh")), None);
+    assert_eq!(terminal_activation(tmp.path(), &s, "/bin/zsh"), None);
+}
+
+#[test]
+fn terminal_activation_for_windows_shell_paths() {
+    let tmp = tempfile::tempdir().unwrap();
+    let mut s = Settings::default();
+    s.languages.python.interpreter = fake_venv(tmp.path(), ".venv with spaces 'quoted'").to_string_lossy().into_owned();
+    let bin = tmp.path().join(".venv with spaces 'quoted'").join(bin_dir());
+    for (shell, script, powershell) in [
+        (r"C:\Program Files\PowerShell\7\pwsh.exe", "Activate.ps1", true),
+        (r"C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe", "Activate.ps1", true),
+        (r"C:\Windows\System32\cmd.exe", "activate.bat", false),
+    ] {
+        assert_eq!(terminal_activation(tmp.path(), &s, shell), None, "missing {script}");
+        let path = bin.join(script);
+        std::fs::write(&path, "").unwrap();
+        let expected = if powershell {
+            format!("& '{}'", path.to_string_lossy().replace('\'', "''"))
+        } else {
+            format!("\"{}\"", path.display())
+        };
+        assert_eq!(terminal_activation(tmp.path(), &s, shell), Some(expected), "{shell}");
+        std::fs::remove_file(path).unwrap();
+    }
+    assert_eq!(terminal_activation(tmp.path(), &s, ""), None);
+    assert_eq!(terminal_activation(tmp.path(), &s, "   "), None);
 }
 
 #[test]
@@ -514,12 +540,12 @@ fn build_dependencies_resolve_to_local_jars() {
         std::fs::write(&p, "").unwrap();
         p
     };
-    touch(m2.join("com/google/guava/guava/33.0/guava-33.0.jar"));
-    let guava_src = touch(m2.join("com/google/guava/guava/33.0/guava-33.0-sources.jar"));
+    let guava = touch(m2.join("com/google/guava/guava/33.0/guava-33.0.jar"));
+    touch(m2.join("com/google/guava/guava/33.0/guava-33.0-sources.jar"));
     let junit = touch(m2.join("junit/junit/4.13/junit-4.13.jar"));
     let files = gradle.join("caches/modules-2/files-2.1/org.slf4j/slf4j-api/2.0.9");
-    touch(files.join("a1b2/slf4j-api-2.0.9.jar"));
-    let slf4j_src = touch(files.join("c3d4/slf4j-api-2.0.9-sources.jar"));
+    let slf4j = touch(files.join("a1b2/slf4j-api-2.0.9.jar"));
+    touch(files.join("c3d4/slf4j-api-2.0.9-sources.jar"));
     let dep = |gradle: bool, g: &str, a: &str, v: &str| BuildDependency {
         gradle,
         group: g.into(),
@@ -540,14 +566,14 @@ fn build_dependencies_resolve_to_local_jars() {
     assert_eq!(
         shown,
         [
-            ("Maven: com.google.guava:guava:33.0", "maven", "guava-33.0-sources.jar"),
+            ("Maven: com.google.guava:guava:33.0", "maven", "guava-33.0.jar"),
             ("Maven: junit:junit:4.13", "maven", "junit-4.13.jar"),
-            ("Gradle: org.slf4j:slf4j-api:2.0.9", "gradle", "slf4j-api-2.0.9-sources.jar"),
+            ("Gradle: org.slf4j:slf4j-api:2.0.9", "gradle", "slf4j-api-2.0.9.jar"),
         ]
     );
-    assert_eq!(groups[0].roots[0].path, ide_core::IpcPath::from(ide_vfs::archive_root(&guava_src)));
+    assert_eq!(groups[0].roots[0].path, ide_core::IpcPath::from(ide_vfs::archive_root(&guava)));
     assert_eq!(groups[1].roots[0].path, ide_core::IpcPath::from(ide_vfs::archive_root(&junit)));
-    assert_eq!(groups[2].roots[0].path, ide_core::IpcPath::from(ide_vfs::archive_root(&slf4j_src)));
+    assert_eq!(groups[2].roots[0].path, ide_core::IpcPath::from(ide_vfs::archive_root(&slf4j)));
     // A Gradle build also finds jars installed in the Maven local repository (`mavenLocal()`).
     let groups = dependency_libraries(&[dep(true, "junit", "junit", "4.13")], Some(&m2), Some(&gradle));
     assert_eq!(groups[0].name, "Gradle: junit:junit:4.13");
diff --git a/crates/ide-terminal/src/lib.rs b/crates/ide-terminal/src/lib.rs
index d651b23be..9caadf583 100644
--- a/crates/ide-terminal/src/lib.rs
+++ b/crates/ide-terminal/src/lib.rs
@@ -497,7 +497,7 @@ pub fn available_shells() -> Vec<String> {
 
 /// Picks the shell binary and its arguments. A default (or explicitly chosen but
 /// argument-less) POSIX shell is started as a login shell, like Terminal.app/IDEA.
-fn resolve_shell(shell: Option<&str>, args: &[String]) -> (String, Vec<String>) {
+pub fn resolve_shell(shell: Option<&str>, args: &[String]) -> (String, Vec<String>) {
     let shell = shell.map(str::trim).filter(|s| !s.is_empty()).map(str::to_owned).unwrap_or_else(default_shell);
     if !args.is_empty() {
         return (shell, args.to_vec());
@@ -808,8 +808,12 @@ mod tests {
         assert_eq!((shell.as_str(), args), ("/bin/zsh", vec!["-l".to_owned()]));
         let (_, args) = resolve_shell(Some("/usr/bin/python3"), &[]);
         assert!(args.is_empty());
-        let (_, args) = resolve_shell(None, &[]);
-        assert_eq!(args, vec!["-l".to_owned()]);
+        for configured in [None, Some(""), Some(" \t ")] {
+            let (shell, args) = resolve_shell(configured, &[]);
+            assert_eq!(shell, default_shell_path());
+            assert_eq!(args, vec!["-l".to_owned()]);
+        }
+        assert_eq!(resolve_shell(Some(" /bin/bash "), &["-i".into()]), ("/bin/bash".into(), vec!["-i".into()]));
         assert_eq!(shell_title("C:\\Program Files\\PowerShell\\7\\pwsh.exe"), "pwsh");
         let env = terminal_env(&BTreeMap::from([("TERM".into(), "dumb".into())]));
         assert_eq!(env["TERM"], "dumb");
diff --git a/crates/ide-tools/src/bundled.rs b/crates/ide-tools/src/bundled.rs
new file mode 100644
index 000000000..03cbbb875
--- /dev/null
+++ b/crates/ide-tools/src/bundled.rs
@@ -0,0 +1,28 @@
+//! Versioned app-owned plugin jars, shared by tool detection and language-server launches.
+
+use crate::{Method, ToolSpec};
+use std::path::{Path, PathBuf};
+
+pub(crate) fn install(root: &Path, spec: &ToolSpec) -> std::io::Result<PathBuf> {
+    let Method::Bundled { filename, bytes, .. } = spec.method else { unreachable!("bundled tool") };
+    let dir = root.join(spec.name).join("bin");
+    // The agent path participates in the JDT LS workspace key: upgrades must
+    // discard incremental state compiled with the previous agent.
+    let path = dir.join(filename);
+    if std::fs::read(&path).is_ok_and(|old| old == bytes) {
+        return Ok(path);
+    }
+    std::fs::create_dir_all(&dir)?;
+    let nonce = std::time::SystemTime::now().duration_since(std::time::UNIX_EPOCH).unwrap_or_default().as_nanos();
+    let temporary = dir.join(format!(".{filename}-{}-{nonce}.tmp", std::process::id()));
+    let result = std::fs::write(&temporary, bytes).and_then(|_| std::fs::rename(&temporary, &path));
+    if let Err(error) = result {
+        let _ = std::fs::remove_file(&temporary);
+        // Another window may have installed the same bytes concurrently.
+        if !std::fs::read(&path).is_ok_and(|old| old == bytes) {
+            tracing::warn!(tool = spec.name, %error, "Bundled plugin unavailable");
+            return Err(error);
+        }
+    }
+    Ok(path)
+}
diff --git a/crates/ide-tools/src/formatter.rs b/crates/ide-tools/src/formatter.rs
new file mode 100644
index 000000000..9b599f0bb
--- /dev/null
+++ b/crates/ide-tools/src/formatter.rs
@@ -0,0 +1,174 @@
+//! External formatting: resolve a tool, pass unsaved text on stdin, return text without writing files.
+
+use crate::Tools;
+use ide_core::{CancellationToken, IdeError, IdeResult};
+use ide_language::FormatterConfig;
+use std::ffi::OsString;
+use std::path::{Path, PathBuf};
+use std::process::Command;
+use std::time::Duration;
+
+/// Walk from the file's directory upward, including workspace parents (monorepos).
+pub fn find_up(file: &Path, relative: &Path) -> Option<PathBuf> {
+    file.parent()?.ancestors().map(|dir| dir.join(relative)).find(|p| p.is_file())
+}
+
+fn package_bin(package: &Path) -> IdeResult<PathBuf> {
+    let json: serde_json::Value = serde_json::from_slice(&std::fs::read(package.join("package.json"))?)
+        .map_err(|e| IdeError::invalid(format!("Prettier: {e}")))?;
+    let bin = json["bin"]
+        .as_str()
+        .or_else(|| json["bin"]["prettier"].as_str())
+        .ok_or_else(|| IdeError::invalid("Prettier: package has no CLI entry point"))?;
+    let path = package.join(bin);
+    if !path.is_file() {
+        return Err(IdeError::unavailable(format!("Prettier: CLI does not exist: {}", path.display())));
+    }
+    Ok(path)
+}
+
+impl Tools {
+    /// Explicit executable/script, then the nearest project package, then managed tools and PATH.
+    pub fn formatter_command(&self, tool: &str, file: &Path, custom: Option<&Path>) -> IdeResult<Command> {
+        self.resolve_formatter_command(tool, file, custom).map_err(|e| e.with_tool(tool))
+    }
+
+    fn resolve_formatter_command(&self, tool: &str, file: &Path, custom: Option<&Path>) -> IdeResult<Command> {
+        if tool != "prettier" {
+            return Err(IdeError::unavailable(format!("Unknown external formatter: {tool}")));
+        }
+        let (path, node) = if let Some(custom) = custom.filter(|p| p.is_dir()) {
+            (package_bin(custom)?, true)
+        } else if let Some(custom) = custom {
+            (custom.to_path_buf(), matches!(custom.extension().and_then(|s| s.to_str()), Some("js" | "cjs" | "mjs")))
+        } else if let Some(manifest) = find_up(file, Path::new("node_modules/prettier/package.json")) {
+            (package_bin(manifest.parent().unwrap())?, true)
+        } else if self.root.join("node_modules/prettier/package.json").is_file() {
+            (package_bin(&self.root.join("node_modules/prettier"))?, true)
+        } else {
+            (self.which("prettier").ok_or_else(|| IdeError::missing_tool("prettier"))?, false)
+        };
+        if node {
+            let node = self.which("node").ok_or_else(|| IdeError::unavailable("Prettier: Node.js is required"))?;
+            let mut cmd = self.command(node);
+            cmd.arg(path);
+            Ok(cmd)
+        } else {
+            Ok(self.command(path))
+        }
+    }
+}
+
+/// Project configuration overrides these defaults; Prettier resolves config and plugins itself.
+pub fn arguments(
+    config: &FormatterConfig,
+    file: &Path,
+    tab_size: u32,
+    insert_spaces: bool,
+    range: Option<(u32, u32)>,
+) -> Vec<OsString> {
+    let parser = if config.parser == "markdown" && file.extension().is_some_and(|s| s == "mdx") {
+        "mdx"
+    } else {
+        &config.parser
+    };
+    let mut args: Vec<OsString> = [
+        "--parser",
+        parser,
+        "--config-precedence",
+        "file-override",
+        "--tab-width",
+        &tab_size.max(1).to_string(),
+        "--use-tabs",
+        if insert_spaces { "false" } else { "true" },
+    ]
+    .into_iter()
+    .map(Into::into)
+    .collect();
+    args.extend(["--stdin-filepath".into(), file.as_os_str().to_owned()]);
+    if config.range
+        && let Some((start, end)) = range
+    {
+        args.extend(["--range-start".into(), start.to_string().into(), "--range-end".into(), end.to_string().into()]);
+    }
+    // CLI defaults only find ignores in cwd; explicitly pass the nearest ancestor's files.
+    for name in [".prettierignore", ".gitignore"] {
+        if let Some(path) = find_up(file, Path::new(name)) {
+            args.extend(["--ignore-path".into(), path.into_os_string()]);
+        }
+    }
+    args
+}
+
+pub fn run(mut command: Command, text: &str, cancel: &CancellationToken) -> IdeResult<String> {
+    crate::process::run_input(&mut command, text, Duration::from_secs(15), cancel).map_err(|e| e.with_tool("prettier"))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn missing_formatter_is_structured_but_invalid_custom_path_is_not_an_install_prompt() {
+        use ide_core::error::{ErrorData, ErrorKind};
+        let dir = tempfile::tempdir().unwrap();
+        let tools = Tools::with_paths(dir.path().join("tools"), OsString::new(), crate::platform::Platform::current());
+        let file = dir.path().join("file.md");
+        let missing = tools.formatter_command("prettier", &file, None).unwrap_err();
+        assert_eq!(missing.kind, ErrorKind::NotFound);
+        assert_eq!(missing.data, Some(ErrorData::Tool { tool: "prettier".into(), missing: true }));
+        let custom = tools.formatter_command("prettier", &file, Some(&dir.path().join("absent-prettier"))).unwrap();
+        let failure = run(custom, "text", &Default::default()).unwrap_err();
+        assert_eq!(failure.data, Some(ErrorData::Tool { tool: "prettier".into(), missing: false }));
+    }
+
+    #[cfg(unix)]
+    #[test]
+    fn stderr_is_preserved_verbatim_even_when_longer_than_four_thousand_characters() {
+        let mut command = Command::new("sh");
+        command.args(["-c", "i=0; while [ $i -lt 1000 ]; do printf 'error\\n' >&2; i=$((i+1)); done; exit 1"]);
+        let failure = run(command, "", &Default::default()).unwrap_err();
+        assert_eq!(failure.message, "error\n".repeat(1000));
+        assert_eq!(failure.data, Some(ide_core::error::ErrorData::Tool { tool: "prettier".into(), missing: false }));
+    }
+
+    #[test]
+    fn discovers_nearest_package_and_ignore_above_nested_file() {
+        let dir = tempfile::tempdir().unwrap();
+        let root = dir.path();
+        std::fs::create_dir_all(root.join("packages/web/src")).unwrap();
+        std::fs::write(root.join(".prettierignore"), "ignored.md").unwrap();
+        std::fs::create_dir_all(root.join("node_modules/prettier")).unwrap();
+        std::fs::write(root.join("node_modules/prettier/package.json"), "{}").unwrap();
+        let file = root.join("packages/web/src/readme.md");
+        assert_eq!(find_up(&file, Path::new(".prettierignore")), Some(root.join(".prettierignore")));
+        std::fs::write(root.join("packages/web/.prettierignore"), "src/ignored.md").unwrap();
+        assert_eq!(find_up(&file, Path::new(".prettierignore")), Some(root.join("packages/web/.prettierignore")));
+        assert_eq!(
+            find_up(&file, Path::new("node_modules/prettier/package.json")),
+            Some(root.join("node_modules/prettier/package.json"))
+        );
+    }
+
+    #[test]
+    fn arguments_use_stdin_config_precedence_and_only_supported_ranges() {
+        for (parser, supports_range) in [
+            ("markdown", false),
+            ("css", false),
+            ("yaml", false),
+            ("typescript", true),
+            ("graphql", true),
+            ("vue", true),
+        ] {
+            let config = FormatterConfig { tool: "prettier".into(), parser: parser.into(), range: supports_range };
+            let args = arguments(&config, Path::new("/project with spaces/file.md"), 4, false, Some((3, 9)));
+            let args: Vec<_> = args.iter().map(|a| a.to_string_lossy()).collect();
+            assert!(args.windows(2).any(|a| a == ["--config-precedence", "file-override"]));
+            assert!(args.windows(2).any(|a| a == ["--stdin-filepath", "/project with spaces/file.md"]));
+            assert!(args.windows(2).any(|a| a == ["--tab-width", "4"]));
+            assert!(args.windows(2).any(|a| a == ["--use-tabs", "true"]));
+            assert_eq!(args.contains(&"--range-start".into()), supports_range);
+            assert!(!args.contains(&"--write".into()));
+        }
+    }
+}
diff --git a/crates/ide-tools/src/lib.rs b/crates/ide-tools/src/lib.rs
index d5cd36c0d..1822367fe 100644
--- a/crates/ide-tools/src/lib.rs
+++ b/crates/ide-tools/src/lib.rs
@@ -10,6 +10,8 @@
 //! [`tools_bin_dirs`] on the process `PATH` at startup.
 
 pub mod archive;
+mod bundled;
+pub mod formatter;
 pub mod jdk;
 pub mod platform;
 mod process;
@@ -146,7 +148,7 @@ fn managed_bin_dir(root: &Path, spec: &ToolSpec, platform: Platform) -> Option<P
         Method::PipVenv { .. } => {
             Some(root.join(spec.name).join("venv").join(if platform.os == Os::Windows { "Scripts" } else { "bin" }))
         }
-        Method::Rustup { .. } | Method::PipUser { .. } | Method::PipTarget { .. } => None,
+        Method::Bundled { .. } | Method::Rustup { .. } | Method::PipUser { .. } | Method::PipTarget { .. } => None,
     }
 }
 
@@ -322,6 +324,9 @@ fn usages(langs: &[LanguageConfig]) -> BTreeMap<String, Usage> {
         }
     };
     for l in langs {
+        if let Some(f) = &l.formatter {
+            add(&f.tool, &f.tool, ToolKind::Formatter, None, &l.name);
+        }
         for s in &l.language_servers {
             add(&s.name, &s.command, ToolKind::LanguageServer, s.install_hint.as_ref(), &l.name);
         }
@@ -389,9 +394,12 @@ fn is_bundle(command: &str) -> bool {
     command.ends_with(".jar")
 }
 
-/// Path of an installed plugin bundle (`<tools>/<name>/bin/<jar>`), if present.
+/// Path of an app-provided or installed plugin jar. Embedded jars are materialized on demand.
 pub fn managed_bundle(app_data: &Path, name: &str) -> Option<PathBuf> {
     let spec = registry::find(name)?;
+    if matches!(spec.method, Method::Bundled { .. }) {
+        return bundled::install(&tools_dir(app_data), spec).ok();
+    }
     let jar = spec.commands.first().filter(|c| is_bundle(c))?;
     let path = tools_dir(app_data).join(spec.name).join("bin").join(jar);
     path.is_file().then_some(path)
@@ -542,6 +550,7 @@ impl Tools {
     fn method_missing(&self, method: Method) -> Option<String> {
         let need = |ok: bool, msg: &str| (!ok).then(|| msg.to_string());
         match method {
+            Method::Bundled { .. } => None,
             Method::Rustup { .. } => need(self.which("rustup").is_some(), "rustup is required (https://rustup.rs)"),
             Method::Npm { .. } => need(
                 self.which_any(&["npm", "pnpm"]).is_some(),
@@ -604,7 +613,8 @@ impl Tools {
         };
         let (status, path, version) = self.detect(spec);
         let unavailable_reason = self.unavailable_reason(spec);
-        let can_uninstall = status == ToolStatus::Installed;
+        let bundled = matches!(spec.method, Method::Bundled { .. });
+        let can_uninstall = status == ToolStatus::Installed && !bundled;
         Some(ToolInfo {
             name: spec.name.to_string(),
             display_name: spec.display.to_string(),
@@ -615,7 +625,7 @@ impl Tools {
             path: path.map(Into::into),
             version,
             install_method: Some(self.install_method(spec).label().to_string()),
-            can_install: unavailable_reason.is_none(),
+            can_install: unavailable_reason.is_none() && !bundled,
             unavailable_reason,
             can_uninstall,
             install_hint,
@@ -654,6 +664,12 @@ impl Tools {
     }
 
     fn detect(&self, spec: &ToolSpec) -> (ToolStatus, Option<PathBuf>, Option<String>) {
+        if let Method::Bundled { version, .. } = spec.method {
+            return match bundled::install(&self.root, spec) {
+                Ok(path) => (ToolStatus::Installed, Some(path), Some(version.to_owned())),
+                Err(_) => (ToolStatus::Missing, None, None),
+            };
+        }
         let main = spec.commands[0];
         let managed = managed_bin_dir(&self.root, spec, self.platform).and_then(|d| self.exe_in(&d, main));
         if let Some(path) = managed {
@@ -782,6 +798,9 @@ impl Tools {
             let method = self.install_method(spec);
             emit(InstallEvent::Line { text: format!("Installing {} via {}…", spec.display, method.label()) });
             match method {
+                Method::Bundled { .. } => {
+                    bundled::install(&self.root, spec)?;
+                }
                 Method::Rustup { component } => {
                     let mut c = self.command(self.which("rustup").expect("checked"));
                     c.args(["component", "add", component]);
@@ -1188,6 +1207,8 @@ impl Tools {
         let cancel = CancellationToken::new();
         let quiet = |_: InstallEvent| {};
         match self.install_method(spec) {
+            // App-owned resources remain available for every project/window.
+            Method::Bundled { .. } => {}
             Method::Rustup { component } => {
                 let rustup = self.which("rustup").ok_or_else(|| IdeError::unavailable("rustup not found"))?;
                 let mut c = self.command(rustup);
diff --git a/crates/ide-tools/src/process.rs b/crates/ide-tools/src/process.rs
index cd3e15788..fad1f755d 100644
--- a/crates/ide-tools/src/process.rs
+++ b/crates/ide-tools/src/process.rs
@@ -464,3 +464,120 @@ mod tests {
         assert_eq!(run_quiet(cmd, Duration::from_secs(5)), Some((true, "v1.2.3\n".into())));
     }
 }
+
+/// Runs a formatter with separate pipes so diagnostics can never become document text.
+pub(crate) fn run_input(
+    cmd: &mut Command,
+    input: &str,
+    timeout: Duration,
+    cancel: &CancellationToken,
+) -> IdeResult<String> {
+    use std::io::Write;
+    if cancel.is_cancelled() {
+        return Err(IdeError::cancelled());
+    }
+    let mut child = own_group(cmd).stdin(Stdio::piped()).stdout(Stdio::piped()).stderr(Stdio::piped()).spawn()?;
+    let mut stdin = child.stdin.take().unwrap();
+    let input = input.to_owned();
+    // All pipes drain concurrently, including stdin: large documents cannot deadlock or bypass the timeout.
+    enum Pipe {
+        Written(std::io::Result<()>),
+        Read(bool, std::io::Result<Vec<u8>>),
+    }
+    let (tx, rx) = mpsc::channel();
+    let writer = tx.clone();
+    std::thread::spawn(move || {
+        let _ = writer.send(Pipe::Written(stdin.write_all(input.as_bytes())));
+    });
+    for (is_stderr, mut pipe) in [
+        (false, Box::new(child.stdout.take().unwrap()) as Box<dyn Read + Send>),
+        (true, Box::new(child.stderr.take().unwrap()) as Box<dyn Read + Send>),
+    ] {
+        let tx = tx.clone();
+        std::thread::spawn(move || {
+            let mut bytes = Vec::new();
+            let _ = tx.send(Pipe::Read(is_stderr, pipe.read_to_end(&mut bytes).map(|_| bytes)));
+        });
+    }
+    drop(tx);
+    let started = Instant::now();
+    let (mut status, mut output, mut errors, mut written) = (None, None, None, None);
+    let result = loop {
+        if cancel.is_cancelled() {
+            break Err(IdeError::cancelled());
+        }
+        if started.elapsed() >= timeout {
+            break Err(IdeError::new(ErrorKind::TimedOut, "Formatting timed out"));
+        }
+        if status.is_none() {
+            match child.try_wait() {
+                Ok(s) => status = s,
+                Err(e) => break Err(e.into()),
+            }
+        }
+        if status.is_some() && output.is_some() && errors.is_some() && written.is_some() {
+            break Ok(());
+        }
+        match rx.recv_timeout(Duration::from_millis(10)) {
+            Ok(Pipe::Written(result)) => written = Some(result),
+            Ok(Pipe::Read(true, result)) => errors = Some(result),
+            Ok(Pipe::Read(false, result)) => output = Some(result),
+            Err(mpsc::RecvTimeoutError::Disconnected) if output.is_some() && errors.is_some() && written.is_some() => {
+                std::thread::sleep(Duration::from_millis(10));
+            }
+            Err(mpsc::RecvTimeoutError::Disconnected) => break Err(IdeError::internal("formatter pipe reader failed")),
+            Err(mpsc::RecvTimeoutError::Timeout) => {}
+        }
+    };
+    if result.is_err() {
+        kill(&mut child);
+    }
+    result?;
+    let output = output.unwrap()?;
+    let errors = errors.unwrap()?;
+    let status = status.unwrap();
+    if !status.success() {
+        let diagnostics: String = String::from_utf8_lossy(&errors).into_owned();
+        return Err(IdeError::invalid(if diagnostics.trim().is_empty() {
+            format!("Formatter exited with {status}")
+        } else {
+            diagnostics
+        }));
+    }
+    written.unwrap()?;
+    String::from_utf8(output).map_err(|e| IdeError::invalid(e.to_string()))
+}
+
+#[cfg(all(test, unix))]
+mod input_tests {
+    use super::*;
+
+    #[test]
+    fn separate_diagnostics_and_never_return_failed_output() {
+        let mut command = Command::new("sh");
+        command.args(["-c", "cat; printf warning >&2"]);
+        assert_eq!(run_input(&mut command, "a😀\n", Duration::from_secs(2), &Default::default()).unwrap(), "a😀\n");
+        let mut command = Command::new("sh");
+        command.args(["-c", "printf broken; printf 'invalid syntax' >&2; exit 1"]);
+        let e = run_input(&mut command, "", Duration::from_secs(2), &Default::default()).unwrap_err();
+        assert_eq!(e.message, "invalid syntax");
+    }
+
+    #[test]
+    fn timeout_kills_formatter_and_cancellation_prevents_start() {
+        let mut command = Command::new("sh");
+        command.args(["-c", "sleep 10 &"]);
+        let start = Instant::now();
+        assert_eq!(
+            run_input(&mut command, "", Duration::from_millis(50), &Default::default()).unwrap_err().kind,
+            ErrorKind::TimedOut
+        );
+        assert!(start.elapsed() < Duration::from_secs(2));
+        let cancel = CancellationToken::new();
+        cancel.cancel();
+        assert_eq!(
+            run_input(&mut Command::new("does-not-exist"), "", Duration::from_secs(2), &cancel).unwrap_err().kind,
+            ErrorKind::Cancelled
+        );
+    }
+}
diff --git a/crates/ide-tools/src/registry.rs b/crates/ide-tools/src/registry.rs
index 8bac71906..5c05cbe75 100644
--- a/crates/ide-tools/src/registry.rs
+++ b/crates/ide-tools/src/registry.rs
@@ -12,6 +12,7 @@ pub enum ToolKind {
     Debugger,
     /// Loaded into another tool's process, e.g. a jdtls agent.
     Plugin,
+    Formatter,
 }
 
 /// Where release archives come from.
@@ -31,6 +32,8 @@ pub enum ReleaseSource {
 
 #[derive(Clone, Copy, Debug)]
 pub enum Method {
+    /// An app-owned plugin jar, materialized without a network download.
+    Bundled { filename: &'static str, version: &'static str, bytes: &'static [u8] },
     /// `rustup component add <component>`.
     Rustup { component: &'static str },
     /// npm / pnpm packages installed into `<tools>/node_modules`; the first is the primary one.
@@ -56,6 +59,7 @@ pub enum Method {
 impl Method {
     pub fn label(&self) -> &'static str {
         match self {
+            Method::Bundled { .. } => "Bundled",
             Method::Rustup { .. } => "rustup",
             Method::Npm { .. } => "npm",
             Method::Go { .. } => "go install",
@@ -102,7 +106,7 @@ impl ToolSpec {
 
 use Arch::{Arm64, X64};
 use Os::{Linux, Mac, Windows};
-use ToolKind::{Debugger, LanguageServer, Plugin};
+use ToolKind::{Debugger, Formatter, LanguageServer, Plugin};
 
 const V: Option<(&str, &[&str])> = None;
 const JAVA: &[(&str, &str)] = &[("java", "Java is required (https://adoptium.net)")];
@@ -119,6 +123,17 @@ const fn ver(cmd: &'static str) -> Option<(&'static str, &'static [&'static str]
 pub const TYPESCRIPT: &str = "typescript@6";
 
 pub static TOOLS: &[ToolSpec] = &[
+    ToolSpec {
+        name: "prettier",
+        display: "Prettier",
+        kind: Formatter,
+        commands: &["prettier"],
+        method: Method::Npm { packages: &["prettier"] },
+        fallback: None,
+        version: ver("prettier"),
+        needs: NODE,
+        homepage: "https://prettier.io",
+    },
     ToolSpec {
         name: "rust-analyzer",
         display: "rust-analyzer",
@@ -578,15 +593,13 @@ pub static TOOLS: &[ToolSpec] = &[
         display: "Lombok (jdtls agent)",
         kind: Plugin,
         commands: &["lombok.jar"],
-        // Newer than the Lombok a project pins: old ones fail inside current ECJ.
-        method: Method::Release {
-            source: ReleaseSource::MavenCentral { group: "org.projectlombok", artifact: "lombok" },
-            assets: &[
-                any_arch(Mac, "lombok-*.jar"),
-                any_arch(Linux, "lombok-*.jar"),
-                any_arch(Windows, "lombok-*.jar"),
-            ],
-            locate: &["lombok.jar"],
+        // Equinox removed getModuleClassLoader(boolean), breaking lombok.config lookup.
+        // Return to Maven Central once an official release includes lombok#4059.
+        // Source commit, build instructions and checksum: plugins/lombok/README.md.
+        method: Method::Bundled {
+            filename: "lombok-1.18.48-openidea.1.jar",
+            version: "1.18.48-openidea.1",
+            bytes: include_bytes!("../../../plugins/lombok/lombok-1.18.48-openidea.1.jar"),
         },
         fallback: None,
         version: V,
@@ -942,6 +955,11 @@ mod tests {
                 known.insert((d.adapter.clone(), d.command.clone()));
             }
         }
+        for l in &langs {
+            if let Some(f) = &l.formatter {
+                known.insert((f.tool.clone(), f.tool.clone()));
+            }
+        }
         for t in TOOLS.iter().filter(|t| t.kind != Plugin) {
             assert!(
                 known.contains(&(t.name.to_string(), t.commands[0].to_string())),
diff --git a/crates/ide-tools/src/sources.rs b/crates/ide-tools/src/sources.rs
index 09ec12a4b..2337bc75c 100644
--- a/crates/ide-tools/src/sources.rs
+++ b/crates/ide-tools/src/sources.rs
@@ -434,7 +434,6 @@ mod tests {
         assert_eq!(d.version, "1.18.48");
         assert_eq!(d.name, "lombok-1.18.48.jar");
         assert_eq!(d.url, "https://repo1.maven.org/maven2/org/projectlombok/lombok/1.18.48/lombok-1.18.48.jar");
-        assert!(select_asset(&[d.name.as_str()], find("lombok").unwrap().asset_rules(), LINUX).is_some());
         assert!(maven_pick("g", "a", "<metadata/>").is_err());
         assert!(maven_pick("g", "a", "<release>../x</release>").is_err());
     }
diff --git a/crates/ide-tools/src/tests.rs b/crates/ide-tools/src/tests.rs
index e6aa29c27..00a3c55ea 100644
--- a/crates/ide-tools/src/tests.rs
+++ b/crates/ide-tools/src/tests.rs
@@ -43,6 +43,61 @@ fn find<'a>(list: &'a [ToolInfo], name: &str) -> &'a ToolInfo {
     list.iter().find(|t| t.name == name).unwrap_or_else(|| panic!("{name} not listed"))
 }
 
+#[test]
+fn bundled_lombok_replaces_legacy_installs_on_every_platform_without_downloads() {
+    for os in [Os::Mac, Os::Linux, Os::Windows] {
+        for arch in [platform::Arch::Arm64, platform::Arch::X64] {
+            let env = Env::new();
+            let legacy = env.root.join("lombok/bin/lombok.jar");
+            fs::create_dir_all(legacy.parent().unwrap()).unwrap();
+            fs::write(&legacy, b"old official agent").unwrap();
+            fs::write(env.root.join("lombok").join(MANIFEST), r#"{"version":"1.18.48"}"#).unwrap();
+            let tools = Tools::with_paths(env.root.clone(), OsString::new(), Platform { os, arch });
+            let info = tools.info("lombok", &[]).unwrap();
+            let path = managed_bundle(env.root.parent().unwrap(), "lombok").unwrap();
+            assert_eq!(info.status, ToolStatus::Installed);
+            assert_eq!(info.version.as_deref(), Some("1.18.48-openidea.1"));
+            assert_eq!(info.path, Some(path.clone().into()));
+            assert_eq!(path.file_name().unwrap(), "lombok-1.18.48-openidea.1.jar");
+            assert!(!info.can_install && !info.can_uninstall);
+            assert_eq!(tools.unavailable_reason(registry::find("lombok").unwrap()), None);
+            assert_eq!(fs::read(&legacy).unwrap(), b"old official agent", "other windows may still use it");
+        }
+    }
+}
+
+#[test]
+fn bundled_lombok_is_available_offline_and_repairs_missing_or_corrupt_files() {
+    let env = Env::new();
+    let data = env.root.parent().unwrap();
+    let agent = managed_bundle(data, "lombok").unwrap();
+    let checksum = include_str!("../../../plugins/lombok/SHA256SUMS").split_whitespace().next().unwrap();
+    assert_eq!(sources::sha256_file(&agent).unwrap(), checksum);
+    for contents in [None, Some(b"incomplete jar".as_slice())] {
+        if let Some(contents) = contents {
+            fs::write(&agent, contents).unwrap();
+        } else {
+            fs::remove_file(&agent).unwrap();
+        }
+        assert_eq!(managed_bundle(data, "lombok"), Some(agent.clone()));
+        assert_eq!(sources::sha256_file(&agent).unwrap(), checksum);
+    }
+    assert_eq!(fs::read_dir(agent.parent().unwrap()).unwrap().count(), 1, "no temporary jars left behind");
+}
+
+#[test]
+fn concurrent_windows_get_the_same_complete_bundled_lombok() {
+    let env = Env::new();
+    let data = env.root.parent().unwrap();
+    std::thread::scope(|scope| {
+        let windows: Vec<_> = (0..8).map(|_| scope.spawn(|| managed_bundle(data, "lombok").unwrap())).collect();
+        let paths: Vec<_> = windows.into_iter().map(|window| window.join().unwrap()).collect();
+        assert!(paths.iter().all(|path| path == &paths[0]));
+        let checksum = include_str!("../../../plugins/lombok/SHA256SUMS").split_whitespace().next().unwrap();
+        assert_eq!(sources::sha256_file(&paths[0]).unwrap(), checksum);
+    });
+}
+
 #[test]
 fn version_parsing() {
     assert_eq!(parse_version("rust-analyzer 1.85.0 (4d91de4e 2025-02-17)").as_deref(), Some("1.85.0"));
diff --git a/crates/ide-tools/tests/prettier.rs b/crates/ide-tools/tests/prettier.rs
new file mode 100644
index 000000000..3d622caac
--- /dev/null
+++ b/crates/ide-tools/tests/prettier.rs
@@ -0,0 +1,91 @@
+//! `cargo test -p ide-tools --test prettier -- --ignored --nocapture`
+//! Installs into a temporary managed-tools directory; no repository dependency is added.
+use ide_core::CancellationToken;
+use ide_language::FormatterConfig;
+use ide_tools::{Tools, formatter};
+use std::path::Path;
+
+fn format(
+    tools: &Tools,
+    path: &Path,
+    parser: &str,
+    text: &str,
+    range: Option<(u32, u32)>,
+) -> ide_core::IdeResult<String> {
+    let config = FormatterConfig {
+        tool: "prettier".into(),
+        parser: parser.into(),
+        range: matches!(parser, "typescript" | "json" | "graphql"),
+    };
+    let mut cmd = tools.formatter_command("prettier", path, None)?;
+    cmd.current_dir(path.parent().unwrap());
+    cmd.args(formatter::arguments(&config, path, 4, true, range));
+    formatter::run(cmd, text, &CancellationToken::new())
+}
+
+#[test]
+#[ignore = "requires Node.js/npm and network; installs real Prettier into a temporary managed directory"]
+fn real_prettier_config_ignore_languages_ranges_and_errors() {
+    if std::env::var_os("OPENIDEA_TEST_OFFLINE").is_some() {
+        eprintln!("SKIP real Prettier: OPENIDEA_TEST_OFFLINE is set; npm network access is disabled");
+        return;
+    }
+    let temp = tempfile::tempdir().unwrap();
+    let tools = Tools::new(&temp.path().join("app-data"));
+    let info = tools.info("prettier", &[]).unwrap();
+    if !info.can_install {
+        eprintln!("SKIP real Prettier: {}", info.unavailable_reason.unwrap_or_default());
+        return;
+    }
+    tools.install("prettier", &[], &Default::default(), &|_| {}).expect(
+        "Prettier managed install failed; offline environments may set OPENIDEA_TEST_OFFLINE=1 (reported as SKIP)",
+    );
+    let project = temp.path().join("project with spaces");
+    std::fs::create_dir_all(project.join("docs/nested")).unwrap();
+    let md = project.join("docs/nested/readme.md");
+    let input = "# Title\ntext\n\n| a | b |\n|---|---|\n|1|2|\n\n- a\n - b\n";
+    let output = format(&tools, &md, "markdown", input, None).unwrap();
+    assert!(output.starts_with("# Title\n\ntext\n"), "{output}");
+    assert!(output.contains("| 1   | 2   |"), "{output}");
+    assert!(!md.exists(), "formatting must never write the file");
+    std::fs::write(project.join(".prettierrc"), r#"{"proseWrap":"always","printWidth":24,"tabWidth":2}"#).unwrap();
+    let prose =
+        "This is a long paragraph with several words that should wrap according to the project configuration.\n";
+    assert!(format(&tools, &md, "markdown", prose, None).unwrap().lines().count() > 2);
+    std::fs::write(project.join(".prettierignore"), "docs/nested/readme.md\n").unwrap();
+    assert_eq!(format(&tools, &md, "markdown", input, None).unwrap(), input);
+    std::fs::remove_file(project.join(".prettierignore")).unwrap();
+    std::fs::remove_file(project.join(".prettierrc")).unwrap();
+    assert_eq!(
+        format(&tools, &project.join("a.css"), "css", "a{color:red}", None).unwrap(),
+        "a {\n    color: red;\n}\n"
+    );
+    std::fs::write(project.join("package.json"), r#"{"prettier":{"tabWidth":3,"proseWrap":"never"}}"#).unwrap();
+    assert_eq!(
+        format(&tools, &project.join("a.css"), "css", "a{color:red}", None).unwrap(),
+        "a {\n   color: red;\n}\n"
+    );
+    assert_eq!(format(&tools, &project.join("a.yaml"), "yaml", "a: [1,2]\n", None).unwrap(), "a: [1, 2]\n");
+    let js = "const a={x:1};\nconst b={y:2};\n";
+    let formatted = format(&tools, &project.join("a.ts"), "typescript", js, Some((0, 14))).unwrap();
+    assert!(formatted.starts_with("const a = { x: 1 };"), "{formatted}");
+    assert!(formatted.contains("const b={y:2};"), "{formatted}");
+    assert!(format(&tools, &project.join("bad.css"), "css", "a {", None).is_err());
+    // Nearest project version must win over the managed install, including npm's object-style bin.
+    let package = project.join("node_modules/prettier");
+    std::fs::create_dir_all(&package).unwrap();
+    std::fs::write(package.join("package.json"), r#"{"bin":{"prettier":"cli.cjs"}}"#).unwrap();
+    std::fs::write(
+        package.join("cli.cjs"),
+        "process.stdin.resume(); process.stdin.on('end', () => process.stdout.write('project version\\n')); ",
+    )
+    .unwrap();
+    assert_eq!(format(&tools, &md, "markdown", input, None).unwrap(), "project version\n");
+    std::fs::write(package.join("cli.cjs"), "setInterval(() => {}, 1000)").unwrap();
+    let start = std::time::Instant::now();
+    assert!(format(&tools, &md, "markdown", input, None).unwrap_err().message.contains("timed out"));
+    assert!(start.elapsed() < std::time::Duration::from_secs(20));
+    eprintln!(
+        "PASS: real managed Prettier, config/ignore discovery, editor defaults, YAML/CSS/Markdown, ranges, errors, project precedence, timeout; no disk writes"
+    );
+}
diff --git a/crates/ide-vcs/src/text_encoding.rs b/crates/ide-vcs/src/text_encoding.rs
index 038256a95..768504b6d 100644
--- a/crates/ide-vcs/src/text_encoding.rs
+++ b/crates/ide-vcs/src/text_encoding.rs
@@ -3,7 +3,7 @@ use encoding_rs::{Encoding, UTF_8, UTF_16BE, UTF_16LE};
 use ide_core::{IdeError, IdeResult};
 use std::borrow::Cow;
 
-/// File charset plus an optional reversible ASCII representation (for properties).
+/// File charset plus an optional ASCII representation (for properties).
 /// The host supplies conversion functions so Git and documents share one codec.
 #[derive(Clone, Copy)]
 pub struct TextEncoding {
diff --git a/crates/ide-vfs/src/compare.rs b/crates/ide-vfs/src/compare.rs
new file mode 100644
index 000000000..8f29b1008
--- /dev/null
+++ b/crates/ide-vfs/src/compare.rs
@@ -0,0 +1,505 @@
+//! Disk comparisons use the same excludes and layered ignore files as the project tree.
+use crate::{EntryKind, ExcludeMatcher, rules::GitignoreStack};
+use ide_core::{CancellationToken, IdeError, IdeResult};
+use serde::{Deserialize, Serialize};
+use specta::Type;
+use std::collections::BTreeMap;
+use std::fs;
+use std::io::Read;
+use std::path::{Path, PathBuf};
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize, Type)]
+#[serde(rename_all = "camelCase")]
+pub enum DirectoryCompareStatus {
+    LeftOnly,
+    RightOnly,
+    Different,
+    Equal,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize, Type)]
+#[serde(rename_all = "camelCase")]
+pub struct DirectoryCompareEntry {
+    pub path: String,
+    pub status: DirectoryCompareStatus,
+    pub left_kind: Option<EntryKind>,
+    pub right_kind: Option<EntryKind>,
+    #[specta(optional)]
+    pub left_link: Option<String>,
+    #[specta(optional)]
+    pub right_link: Option<String>,
+}
+
+#[derive(Clone, Debug, Default, Serialize, Deserialize, Type)]
+#[serde(rename_all = "camelCase")]
+pub struct DirectoryCompareProgress {
+    pub scanned: u32,
+    pub compared: u32,
+    pub total: Option<u32>,
+    pub bytes_read: f64,
+    pub path: String,
+}
+
+struct Entry {
+    kind: EntryKind,
+    size: u64,
+    link: Option<PathBuf>,
+}
+
+fn check(cancel: &CancellationToken) -> IdeResult<()> {
+    if cancel.is_cancelled() { Err(IdeError::cancelled()) } else { Ok(()) }
+}
+
+struct Rules {
+    base: PathBuf,
+    excludes: ExcludeMatcher,
+    ignore: GitignoreStack,
+}
+
+impl Rules {
+    fn new(root: &Path, project: Option<&Path>, excludes: &[String]) -> Self {
+        Self {
+            base: project.filter(|p| root.starts_with(p)).unwrap_or(root).to_path_buf(),
+            excludes: ExcludeMatcher::new(excludes),
+            ignore: GitignoreStack::new(root),
+        }
+    }
+
+    fn excluded(&self, path: &Path, dir: bool) -> bool {
+        path.file_name().is_some_and(|n| n == ".git")
+            || self.excludes.is_excluded(path.strip_prefix(&self.base).unwrap_or(path))
+            || self.ignore.is_ignored(path, dir)
+    }
+}
+
+fn scan(
+    root: &Path,
+    rules: &Rules,
+    cancel: &CancellationToken,
+    progress: &mut DirectoryCompareProgress,
+    emit: &impl Fn(DirectoryCompareProgress),
+) -> IdeResult<BTreeMap<String, Entry>> {
+    if !fs::metadata(root)?.is_dir() {
+        return Err(IdeError::invalid(format!("{} is not a directory", root.display())));
+    }
+    let mut result = BTreeMap::new();
+    let mut pending = vec![root.to_path_buf()];
+    while let Some(dir) = pending.pop() {
+        check(cancel)?;
+        for item in fs::read_dir(dir)? {
+            check(cancel)?;
+            let path = item?.path();
+            let meta = fs::symlink_metadata(&path)?;
+            if rules.excluded(&path, meta.is_dir()) {
+                continue;
+            }
+            let kind = if meta.file_type().is_symlink() {
+                EntryKind::Symlink
+            } else if meta.is_dir() {
+                pending.push(path.clone());
+                EntryKind::Dir
+            } else if meta.is_file() {
+                EntryKind::File
+            } else {
+                continue;
+            };
+            let rel = path.strip_prefix(root).map_err(|e| IdeError::internal(e.to_string()))?;
+            let rel = ide_core::ipc_path::to_ipc(rel);
+            let link = if kind == EntryKind::Symlink { Some(fs::read_link(&path)?) } else { None };
+            result.insert(rel.clone(), Entry { kind, size: meta.len(), link });
+            progress.scanned += 1;
+            progress.path = rel;
+            emit(progress.clone());
+        }
+    }
+    Ok(result)
+}
+
+fn hash(
+    path: &Path,
+    cancel: &CancellationToken,
+    progress: &mut DirectoryCompareProgress,
+    emit: &impl Fn(DirectoryCompareProgress),
+) -> IdeResult<gix::hash::ObjectId> {
+    let mut file = fs::File::open(path)?;
+    let mut hash = gix::hash::hasher(gix::hash::Kind::Sha256);
+    let mut buffer = [0; 64 * 1024];
+    loop {
+        check(cancel)?;
+        let len = file.read(&mut buffer)?;
+        if len == 0 {
+            break;
+        }
+        hash.update(&buffer[..len]);
+        progress.bytes_read += len as f64;
+        emit(progress.clone());
+    }
+    hash.try_finalize().map_err(|e| IdeError::internal(e.to_string()))
+}
+
+/// Size checks avoid reading unequal files. Equal-sized files are hashed in bounded,
+/// cancellable chunks; symlinks compare their link text and are never traversed.
+pub fn compare_directories(
+    left: &Path,
+    right: &Path,
+    project: Option<&Path>,
+    excludes: &[String],
+    cancel: &CancellationToken,
+    emit: impl Fn(DirectoryCompareProgress),
+) -> IdeResult<Vec<DirectoryCompareEntry>> {
+    check(cancel)?;
+    let mut progress = DirectoryCompareProgress::default();
+    emit(progress.clone());
+    let l = scan(left, &Rules::new(left, project, excludes), cancel, &mut progress, &emit)?;
+    let r = scan(right, &Rules::new(right, project, excludes), cancel, &mut progress, &emit)?;
+    let mut paths: Vec<_> = l.keys().chain(r.keys()).cloned().collect();
+    paths.sort();
+    paths.dedup();
+    progress.total = Some(paths.len() as u32);
+    let mut rows = BTreeMap::new();
+    for path in paths {
+        check(cancel)?;
+        progress.path.clone_from(&path);
+        let status = match (l.get(&path), r.get(&path)) {
+            (Some(_), None) => DirectoryCompareStatus::LeftOnly,
+            (None, Some(_)) => DirectoryCompareStatus::RightOnly,
+            (Some(a), Some(b)) => {
+                let equal = a.kind == b.kind
+                    && match a.kind {
+                        EntryKind::Dir => true,
+                        EntryKind::Symlink => a.link == b.link,
+                        EntryKind::File => {
+                            a.size == b.size
+                                && hash(&left.join(&path), cancel, &mut progress, &emit)?
+                                    == hash(&right.join(&path), cancel, &mut progress, &emit)?
+                        }
+                    };
+                if equal { DirectoryCompareStatus::Equal } else { DirectoryCompareStatus::Different }
+            }
+            _ => unreachable!(),
+        };
+        rows.insert(
+            path.clone(),
+            DirectoryCompareEntry {
+                path: path.clone(),
+                status,
+                left_kind: l.get(&path).map(|e| e.kind),
+                right_kind: r.get(&path).map(|e| e.kind),
+                left_link: l.get(&path).and_then(|e| e.link.as_ref()).map(|p| p.to_string_lossy().into_owned()),
+                right_link: r.get(&path).and_then(|e| e.link.as_ref()).map(|p| p.to_string_lossy().into_owned()),
+            },
+        );
+        progress.compared += 1;
+        emit(progress.clone());
+    }
+    let changed: Vec<_> =
+        rows.values().filter(|r| r.status != DirectoryCompareStatus::Equal).map(|r| r.path.clone()).collect();
+    for path in changed {
+        for parent in Path::new(&path).ancestors().skip(1) {
+            if let Some(row) = rows.get_mut(&ide_core::ipc_path::to_ipc(parent))
+                && row.status == DirectoryCompareStatus::Equal
+            {
+                row.status = DirectoryCompareStatus::Different;
+            }
+        }
+    }
+    check(cancel)?;
+    Ok(rows.into_values().collect())
+}
+
+/// Merges a subtree without following links inside the comparison roots. Existing files
+/// require explicit overwrite; directory merges preserve destination-only entries.
+pub fn copy_merge(
+    from: &Path,
+    to: &Path,
+    overwrite: bool,
+    project: Option<&Path>,
+    excludes: &[String],
+    roots: (&Path, &Path),
+) -> IdeResult<()> {
+    fn resolve(path: &Path) -> IdeResult<PathBuf> {
+        if path.exists() {
+            return Ok(dunce::canonicalize(path)?);
+        }
+        let parent = path.parent().ok_or_else(|| IdeError::invalid("copy requires an absolute path"))?;
+        Ok(resolve(parent)?.join(path.file_name().ok_or_else(|| IdeError::invalid("missing file name"))?))
+    }
+    if !from.is_absolute() || !to.is_absolute() {
+        return Err(IdeError::invalid("copy requires absolute paths"));
+    }
+    if !from.starts_with(roots.0) || !to.starts_with(roots.1) {
+        return Err(IdeError::invalid("copy paths must belong to the comparison roots"));
+    }
+    let source = resolve(from)?;
+    let target = resolve(to)?;
+    if source.starts_with(&target) || target.starts_with(&source) {
+        return Err(IdeError::invalid("cannot copy overlapping paths"));
+    }
+    for parent in to.ancestors().skip(1) {
+        // The user explicitly selected this root; aliases above it (e.g. /tmp
+        // on macOS) are valid. Links inside the copied subtree are not followed.
+        if to == roots.1 || parent == roots.1 {
+            break;
+        }
+        if fs::symlink_metadata(parent).is_ok_and(|m| m.file_type().is_symlink()) {
+            return Err(IdeError::invalid("cannot copy through a destination symlink"));
+        }
+    }
+    let source_base = project.filter(|p| from.starts_with(p)).or(Some(roots.0));
+    let target_base = project.filter(|p| to.starts_with(p)).or(Some(roots.1));
+    let rules = Rules::new(from, source_base, excludes);
+    let target_rules = Rules::new(to, target_base, excludes);
+    let mut pending = vec![(from.to_path_buf(), to.to_path_buf())];
+    while let Some((src, dst)) = pending.pop() {
+        let meta = fs::symlink_metadata(&src)?;
+        if rules.excluded(&src, meta.is_dir()) || target_rules.excluded(&dst, meta.is_dir()) {
+            continue;
+        }
+        let existing = fs::symlink_metadata(&dst).ok();
+        let merge = meta.is_dir() && existing.as_ref().is_some_and(|m| m.is_dir());
+        if existing.is_some() && !merge && !overwrite {
+            return Err(std::io::Error::new(std::io::ErrorKind::AlreadyExists, dst.display().to_string()).into());
+        }
+        if meta.is_dir() {
+            if existing.is_some() && !merge {
+                crate::delete(&dst)?;
+            }
+            fs::create_dir_all(&dst)?;
+            for entry in fs::read_dir(&src)? {
+                let entry = entry?;
+                pending.push((entry.path(), dst.join(entry.file_name())));
+            }
+        } else {
+            if let Some(parent) = dst.parent() {
+                fs::create_dir_all(parent)?;
+            }
+            // Stage the complete file before touching its destination.
+            static NEXT: std::sync::atomic::AtomicU64 = std::sync::atomic::AtomicU64::new(0);
+            let id = NEXT.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
+            let temp = dst.with_file_name(format!(".openidea-copy-{}-{id}", std::process::id()));
+            let mut staged = false;
+            let result: IdeResult<()> = (|| {
+                #[cfg(windows)]
+                if meta.file_type().is_symlink() {
+                    use std::os::windows::fs::{FileTypeExt, symlink_dir, symlink_file};
+                    let target = fs::read_link(&src)?;
+                    if meta.file_type().is_symlink_dir() {
+                        symlink_dir(target, &temp)?;
+                    } else {
+                        symlink_file(target, &temp)?;
+                    }
+                } else {
+                    crate::copy(&src, &temp)?;
+                }
+                #[cfg(not(windows))]
+                crate::copy(&src, &temp)?;
+                staged = true;
+                // Recheck after staging: another writer may have created the target.
+                if fs::symlink_metadata(&dst).is_ok() {
+                    if !overwrite {
+                        return Err(
+                            std::io::Error::new(std::io::ErrorKind::AlreadyExists, dst.display().to_string()).into()
+                        );
+                    }
+                    crate::delete(&dst)?;
+                }
+                fs::rename(&temp, &dst)?;
+                Ok(())
+            })();
+            if let Err(error) = &result
+                && (staged || error.kind != ide_core::error::ErrorKind::AlreadyExists)
+            {
+                let _ = crate::delete_permanently(&temp);
+            }
+            result?;
+        }
+    }
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use ide_core::error::ErrorKind;
+
+    fn put(root: &Path, path: &str, content: &[u8]) {
+        let path = root.join(path);
+        fs::create_dir_all(path.parent().unwrap()).unwrap();
+        fs::write(path, content).unwrap();
+    }
+
+    #[test]
+    fn reports_add_delete_modify_equal_binary_unicode_empty_and_type_conflicts() {
+        let tmp = tempfile::tempdir().unwrap();
+        let left = tmp.path().join("left");
+        let right = tmp.path().join("right");
+        put(&left, "子目录/仅左.txt", b"left");
+        put(&right, "only-right", b"right");
+        for (path, a, b) in [
+            ("same", b"same".as_slice(), b"same".as_slice()),
+            ("binary", &[0, 255, 10], &[0, 254, 10]),
+            ("size", b"a", b"bb"),
+            ("conflict", b"file", b""),
+        ] {
+            put(&left, path, a);
+            if path == "conflict" {
+                put(&right, "conflict/child", b"child");
+            } else {
+                put(&right, path, b);
+            }
+        }
+        fs::create_dir(left.join("empty")).unwrap();
+        fs::create_dir(right.join("empty")).unwrap();
+        let rows = compare_directories(&left, &right, None, &[], &CancellationToken::new(), |_| {}).unwrap();
+        let status = |path| rows.iter().find(|r| r.path == path).unwrap().status;
+        assert_eq!(status("same"), DirectoryCompareStatus::Equal);
+        assert_eq!(status("empty"), DirectoryCompareStatus::Equal);
+        for path in ["binary", "size", "conflict"] {
+            assert_eq!(status(path), DirectoryCompareStatus::Different);
+        }
+        assert_eq!(status("子目录/仅左.txt"), DirectoryCompareStatus::LeftOnly);
+        assert_eq!(status("only-right"), DirectoryCompareStatus::RightOnly);
+        assert_eq!(status("conflict/child"), DirectoryCompareStatus::RightOnly);
+    }
+
+    #[test]
+    fn applies_project_anchored_excludes_and_layered_ignores() {
+        let tmp = tempfile::tempdir().unwrap();
+        let left = tmp.path().join("left");
+        let right = tmp.path().join("right");
+        for root in [&left, &right] {
+            put(root, "nested/node_modules/x", b"ignored");
+            put(root, "target/x", b"ignored");
+            put(root, ".git/config", b"ignored");
+            put(root, "generated/x", b"ignored");
+            put(root, ".gitignore", b"*.log\n");
+            put(root, "nested/debug.log", b"ignored");
+            put(root, "kept", b"kept");
+        }
+        let excludes = ["**/node_modules", "**/target", "/left/generated", "/right/generated"].map(String::from);
+        let rows =
+            compare_directories(&left, &right, Some(tmp.path()), &excludes, &CancellationToken::new(), |_| {}).unwrap();
+        assert!(
+            rows.iter()
+                .all(|r| !["node_modules", "target", ".git/", "generated", ".log"].iter().any(|p| r.path.contains(p)))
+        );
+        assert!(rows.iter().any(|r| r.path == "kept"));
+    }
+
+    #[test]
+    fn cancellation_stops_before_scan_during_scan_and_during_hashing() {
+        let tmp = tempfile::tempdir().unwrap();
+        let left = tmp.path().join("left");
+        let right = tmp.path().join("right");
+        put(&left, "big", &vec![1; 1024 * 1024]);
+        put(&right, "big", &vec![1; 1024 * 1024]);
+        for phase in 0..3 {
+            let cancel = CancellationToken::new();
+            if phase == 0 {
+                cancel.cancel();
+            }
+            let result = compare_directories(&left, &right, None, &[], &cancel, |p| {
+                if phase == 1 && p.scanned > 0 || phase == 2 && p.bytes_read > 0.0 {
+                    cancel.cancel();
+                }
+            });
+            assert_eq!(result.unwrap_err().kind, ErrorKind::Cancelled);
+        }
+    }
+
+    #[test]
+    fn size_mismatches_are_not_hashed_and_directory_status_tracks_children() {
+        let tmp = tempfile::tempdir().unwrap();
+        let left = tmp.path().join("left");
+        let right = tmp.path().join("right");
+        put(&left, "nested/file", b"a");
+        put(&right, "nested/file", b"ab");
+        let bytes = std::cell::Cell::new(0.0);
+        let rows =
+            compare_directories(&left, &right, None, &[], &CancellationToken::new(), |p| bytes.set(p.bytes_read))
+                .unwrap();
+        assert_eq!(bytes.get(), 0.0);
+        assert!(rows.iter().all(|r| r.status == DirectoryCompareStatus::Different));
+    }
+
+    #[test]
+    fn merges_copies_with_explicit_overwrite_and_keeps_destination_only_files() {
+        let tmp = tempfile::tempdir().unwrap();
+        let left = tmp.path().join("left");
+        let right = tmp.path().join("right");
+        put(&left, "file", b"new");
+        put(&left, "target/ignored", b"ignored");
+        put(&right, "file", b"old");
+        put(&right, "keep", b"keep");
+        assert_eq!(
+            copy_merge(&left, &right, false, None, &["target".into()], (&left, &right)).unwrap_err().kind,
+            ErrorKind::AlreadyExists
+        );
+        assert_eq!(fs::read(right.join("file")).unwrap(), b"old");
+        copy_merge(&left, &right, true, None, &["target".into()], (&left, &right)).unwrap();
+        assert_eq!(fs::read(right.join("file")).unwrap(), b"new");
+        assert_eq!(fs::read(right.join("keep")).unwrap(), b"keep");
+        assert!(!right.join("target").exists());
+        for (from, to) in [(&left, left.clone()), (&left, left.join("child")), (&right, tmp.path().to_path_buf())] {
+            assert_eq!(
+                copy_merge(from, &to, true, None, &[], (tmp.path(), tmp.path())).unwrap_err().kind,
+                ErrorKind::InvalidInput
+            );
+        }
+    }
+
+    #[test]
+    fn subtree_copy_keeps_excludes_anchored_to_each_comparison_root() {
+        let tmp = tempfile::tempdir().unwrap();
+        let left = tmp.path().join("left");
+        let right = tmp.path().join("right");
+        put(&left, "sub/build/keep", b"included below sub");
+        put(&left, "sub/protected", b"do not overwrite");
+        put(&right, "sub/protected", b"keep destination");
+        put(&right, ".gitignore", b"sub/protected\n");
+        copy_merge(&left.join("sub"), &right.join("sub"), true, None, &["/build".into()], (&left, &right)).unwrap();
+        assert_eq!(fs::read(right.join("sub/build/keep")).unwrap(), b"included below sub");
+        assert_eq!(fs::read(right.join("sub/protected")).unwrap(), b"keep destination");
+    }
+
+    #[test]
+    fn confirmed_copy_replaces_file_directory_type_conflicts() {
+        let tmp = tempfile::tempdir().unwrap();
+        let left = tmp.path().join("left");
+        let right = tmp.path().join("right");
+        put(&left, "file", b"file");
+        put(&right, "file/child", b"old directory");
+        put(&left, "tree/child", b"new directory");
+        put(&right, "tree", b"old file");
+        for path in ["file", "tree"] {
+            copy_merge(&left.join(path), &right.join(path), true, None, &[], (&left, &right)).unwrap();
+        }
+        assert_eq!(fs::read(right.join("file")).unwrap(), b"file");
+        assert_eq!(fs::read(right.join("tree/child")).unwrap(), b"new directory");
+    }
+
+    #[cfg(unix)]
+    #[test]
+    fn symlinks_compare_link_text_and_are_not_followed_when_copying() {
+        use std::os::unix::fs::symlink;
+        let tmp = tempfile::tempdir().unwrap();
+        let left = tmp.path().join("left");
+        let right = tmp.path().join("right");
+        fs::create_dir(&left).unwrap();
+        fs::create_dir(&right).unwrap();
+        symlink(".", left.join("loop")).unwrap();
+        symlink("missing", right.join("loop")).unwrap();
+        let rows = compare_directories(&left, &right, None, &[], &CancellationToken::new(), |_| {}).unwrap();
+        assert_eq!(rows.len(), 1);
+        assert_eq!(rows[0].status, DirectoryCompareStatus::Different);
+        copy_merge(&left.join("loop"), &right.join("copied"), false, None, &[], (&left, &right)).unwrap();
+        assert_eq!(fs::read_link(right.join("copied")).unwrap(), PathBuf::from("."));
+        symlink(&right, tmp.path().join("alias")).unwrap();
+        assert_eq!(
+            copy_merge(&left.join("loop"), &tmp.path().join("alias/new"), true, None, &[], (tmp.path(), tmp.path()))
+                .unwrap_err()
+                .kind,
+            ErrorKind::InvalidInput
+        );
+    }
+}
diff --git a/crates/ide-vfs/src/encoding.rs b/crates/ide-vfs/src/encoding.rs
index 05504a1b2..92e0d999b 100644
--- a/crates/ide-vfs/src/encoding.rs
+++ b/crates/ide-vfs/src/encoding.rs
@@ -62,20 +62,19 @@ pub fn decode_properties_escapes(text: &str) -> String {
 }
 
 /// Serializes displayed properties text as ASCII, using uppercase UTF-16 units.
+/// Existing ASCII Unicode escapes retain their spelling and meaning on disk.
 pub fn encode_properties_ascii(text: &str) -> String {
     use std::fmt::Write;
     let mut out = String::with_capacity(text.len());
     let mut rest = text;
     while let Some(c) = rest.chars().next() {
-        let current = rest;
         rest = &rest[c.len_utf8()..];
         if c == '\\' {
             if rest.starts_with('\\') {
                 out.push_str("\\\\");
                 rest = &rest[1..];
-            } else if unicode_character(current).is_some() || rest.chars().next().is_some_and(|next| !next.is_ascii()) {
-                // Keep a literal backslash from swallowing a generated escape,
-                // or becoming a Unicode escape on the next load.
+            } else if rest.chars().next().is_some_and(|next| !next.is_ascii()) {
+                // Keep a literal backslash from swallowing a generated escape.
                 out.push_str("\\u005C");
             } else {
                 out.push(c);
@@ -387,13 +386,32 @@ mod tests {
         for text in ["plain=ASCII\r\n", r"escaped=\\u0041", r"bad=\u12xz", r"bad=\uD800"] {
             assert_eq!(encode_properties_ascii(text), text);
         }
-        for text in ["你好😀", "\0", "\\中", "\\\\中", "\\\\\\😀", r"\u0041", r"\\u0041", r"\uD83D\uDE00"] {
+        for text in ["你好😀", "\0", "\\中", "\\\\中", "\\\\\\😀", r"\\u0041"] {
             let ascii = encode_properties_ascii(text);
             assert!(ascii.is_ascii());
             assert_eq!(decode_properties_escapes(&ascii), text, "{ascii}");
         }
     }
 
+    #[test]
+    fn properties_ascii_escapes_are_not_escaped_again() {
+        for text in [
+            r"test.key2=\u4F60\u597D",
+            r"test.key3=\u4f60\u597d",
+            r"ascii=\u0041\u005C\u000A",
+            r"emoji=\uD83D\uDE00",
+            r"slashes=\\u4F60 \\\u4F60 \\\\u4F60",
+            r"bad=\u123 \u12xz \uu0041 \uD800 \uDC00",
+        ] {
+            assert_eq!(encode_properties_ascii(text), text, "{text}");
+        }
+        let mixed = "raw=\\u4f60\\u597d; native=你好😀";
+        let expected = r"raw=\u4f60\u597d; native=\u4F60\u597D\uD83D\uDE00";
+        assert_eq!(encode_properties_ascii(mixed), expected);
+        assert_eq!(encode_properties_ascii(expected), expected);
+        assert_eq!(decode_properties_escapes(expected), "raw=你好; native=你好😀");
+    }
+
     #[test]
     fn properties_line_terminator_escapes_survive_an_edit() {
         let source = r"key=one\u000Atwo\u000Dthree";
diff --git a/crates/ide-vfs/src/lib.rs b/crates/ide-vfs/src/lib.rs
index 55c28b71b..6ac24e21b 100644
--- a/crates/ide-vfs/src/lib.rs
+++ b/crates/ide-vfs/src/lib.rs
@@ -2,6 +2,7 @@
 
 mod archive;
 mod bytes;
+mod compare;
 mod encoding;
 mod ops;
 mod rules;
@@ -20,6 +21,9 @@ pub use archive::{
     read_archive_entry, split_archive_path,
 };
 pub use bytes::{ByteRange, FileProbe, MAX_RANGE_LEN, base64, image_mime, probe, read_data_url, read_range};
+pub use compare::{
+    DirectoryCompareEntry, DirectoryCompareProgress, DirectoryCompareStatus, compare_directories, copy_merge,
+};
 use encoding::SNIFF_LEN;
 pub use encoding::{
     LARGE_FILE_THRESHOLD, MAX_OPEN_SIZE, READ_ONLY_THRESHOLD, decode_properties_escapes, encode,
diff --git a/crates/ide-workspace/tests/documents.rs b/crates/ide-workspace/tests/documents.rs
index 028617eb8..02370eed5 100644
--- a/crates/ide-workspace/tests/documents.rs
+++ b/crates/ide-workspace/tests/documents.rs
@@ -641,6 +641,57 @@ fn properties_conversion_uses_displayed_utf16_and_survives_reload() {
     assert!(!f.docs.is_dirty(doc.id).unwrap());
 }
 
+#[test]
+fn properties_pasted_escapes_survive_save_and_decode_on_reload() {
+    let pasted = "test.key1=Hello\ntest.key2=\\u4F60\\u597D\ntest.key3=\\u4f60\\u597d\n";
+    let displayed = "test.key1=Hello\ntest.key2=你好\ntest.key3=你好\n";
+    for encoding in ["utf-8", "iso-8859-1", "utf-16le"] {
+        for eol in ["\n", "\r\n"] {
+            let f = fixture();
+            let path = f.root.join("test_zh_CN.properties");
+            let source = pasted.replace('\n', eol);
+            fs::write(&path, ide_vfs::encode(&source, encoding, encoding == "utf-16le").unwrap()).unwrap();
+            let mut defaults = f.docs.file_defaults();
+            defaults.native_to_ascii = true;
+            defaults.properties_fallback = encoding.into();
+            f.docs.set_file_defaults(defaults.clone());
+            let doc = f.docs.open(&path).unwrap();
+            assert_eq!(doc.text, displayed);
+
+            f.docs.replace_all(doc.id, pasted).unwrap();
+            f.docs.save(doc.id).unwrap();
+            assert_eq!(fs::read(&path).unwrap(), source.as_bytes(), "{encoding} {eol:?}");
+            assert_eq!(f.docs.snapshot(doc.id).unwrap().text, pasted);
+            assert!(!f.docs.is_dirty(doc.id).unwrap());
+            f.docs.on_disk_changed(std::slice::from_ref(&path));
+            assert_eq!(f.docs.snapshot(doc.id).unwrap().text, pasted, "own saves do not reload");
+
+            f.docs.close(doc.id);
+            let reopened = f.docs.open(&path).unwrap();
+            assert_eq!(reopened.text, displayed);
+            // An edit followed by its inverse preserves the original escape casing.
+            f.docs.replace_all(reopened.id, pasted).unwrap();
+            f.docs.replace_all(reopened.id, displayed).unwrap();
+            f.docs.save(reopened.id).unwrap();
+            assert_eq!(fs::read(&path).unwrap(), source.as_bytes());
+
+            let external = format!("{source}test.key4=\\uD83D\\uDE00{eol}");
+            fs::write(&path, &external).unwrap();
+            f.docs.on_disk_changed(std::slice::from_ref(&path));
+            assert_eq!(f.docs.snapshot(reopened.id).unwrap().text, format!("{displayed}test.key4=😀\n"));
+            defaults.native_to_ascii = false;
+            f.docs.set_file_defaults(defaults.clone());
+            f.docs.reload_properties();
+            assert_eq!(f.docs.snapshot(reopened.id).unwrap().text, external.replace("\r\n", "\n"));
+            defaults.native_to_ascii = true;
+            f.docs.set_file_defaults(defaults);
+            f.docs.reload_properties();
+            assert_eq!(f.docs.snapshot(reopened.id).unwrap().text, format!("{displayed}test.key4=😀\n"));
+            assert_eq!(fs::read_to_string(&path).unwrap(), external);
+        }
+    }
+}
+
 #[test]
 fn properties_toggle_reloads_only_clean_properties_and_pins_dirty_codec() {
     let f = fixture();
diff --git a/languages/css.toml b/languages/css.toml
index 81379d5b8..4f8ba1e11 100644
--- a/languages/css.toml
+++ b/languages/css.toml
@@ -1,5 +1,6 @@
 id = "css"
 name = "CSS"
+formatter = { tool = "prettier", parser = "css", range = false }
 extensions = ["css", "pcss", "postcss"]
 block-comment = ["/*", "*/"]
 indent = { tab-size = 2, insert-spaces = true }
diff --git a/languages/graphql.toml b/languages/graphql.toml
index d3a7a9263..a26bb6acd 100644
--- a/languages/graphql.toml
+++ b/languages/graphql.toml
@@ -1,5 +1,6 @@
 id = "graphql"
 name = "GraphQL"
+formatter = { tool = "prettier", parser = "graphql", range = true }
 extensions = ["graphql", "graphqls", "gql"]
 line-comment = "#"
 indent = { tab-size = 2, insert-spaces = true }
diff --git a/languages/html.toml b/languages/html.toml
index 9da5321dd..908771a2d 100644
--- a/languages/html.toml
+++ b/languages/html.toml
@@ -1,5 +1,6 @@
 id = "html"
 name = "HTML"
+formatter = { tool = "prettier", parser = "html", range = false }
 extensions = ["html", "htm", "xhtml", "shtml", "html.tmpl"]
 first-line = "^\\s*<!(?i:doctype)\\s+html"
 block-comment = ["<!--", "-->"]
diff --git a/languages/java.toml b/languages/java.toml
index 7e2e87c7f..7e7837b08 100644
--- a/languages/java.toml
+++ b/languages/java.toml
@@ -32,7 +32,7 @@ resolveAdditionalTextEditsSupport = true
 
 [language-servers.initialization-options.settings.java]
 autobuild = { enabled = true }
-contentProvider = { preferred = "fernflower" }
+contentProvider = { preferred = "fernflowerContentProvider" }
 maven = { downloadSources = true, updateSnapshots = false }
 eclipse = { downloadSources = true }
 references = { includeDecompiledSources = true }
diff --git a/languages/javascript.toml b/languages/javascript.toml
index edbd83d89..b5676537e 100644
--- a/languages/javascript.toml
+++ b/languages/javascript.toml
@@ -1,5 +1,6 @@
 id = "javascript"
 name = "JavaScript"
+formatter = { tool = "prettier", parser = "babel", range = true }
 extensions = ["js", "mjs", "cjs"]
 first-line = "^#!.*\\b(node|nodejs|deno|bun)\\b"
 line-comment = "//"
diff --git a/languages/javascriptreact.toml b/languages/javascriptreact.toml
index f2864cdf3..3c5a17760 100644
--- a/languages/javascriptreact.toml
+++ b/languages/javascriptreact.toml
@@ -1,5 +1,6 @@
 id = "javascriptreact"
 name = "JavaScript JSX"
+formatter = { tool = "prettier", parser = "babel", range = true }
 extensions = ["jsx"]
 line-comment = "//"
 block-comment = ["/*", "*/"]
diff --git a/languages/json.toml b/languages/json.toml
index bad607263..f7010dffa 100644
--- a/languages/json.toml
+++ b/languages/json.toml
@@ -1,5 +1,6 @@
 id = "json"
 name = "JSON"
+formatter = { tool = "prettier", parser = "json", range = true }
 extensions = ["json", "geojson", "topojson", "webmanifest", "har", "avsc", "jsonl", "ndjson", "json.map"]
 filenames = [".prettierrc", ".watchmanconfig", "composer.lock", ".arcconfig"]
 indent = { tab-size = 2, insert-spaces = true }
diff --git a/languages/jsonc.toml b/languages/jsonc.toml
index 272f5c956..d90e5a655 100644
--- a/languages/jsonc.toml
+++ b/languages/jsonc.toml
@@ -1,5 +1,6 @@
 id = "jsonc"
 name = "JSON with Comments"
+formatter = { tool = "prettier", parser = "jsonc", range = true }
 extensions = ["jsonc", "code-workspace", "code-snippets"]
 filenames = ["tsconfig.json", "jsconfig.json", "tsconfig.*.json", "jsconfig.*.json", ".eslintrc", ".eslintrc.json", ".jshintrc", ".babelrc", ".swcrc", "devcontainer.json", ".devcontainer.json", "launch.json", "tasks.json", "settings.json", "extensions.json", "keybindings.json", "tslint.json", "api-extractor.json", "typedoc.json", "deno.json", "biome.json", "turbo.json", "language-configuration.json"]
 line-comment = "//"
diff --git a/languages/less.toml b/languages/less.toml
index 227590f9f..cfc834ee8 100644
--- a/languages/less.toml
+++ b/languages/less.toml
@@ -1,5 +1,6 @@
 id = "less"
 name = "Less"
+formatter = { tool = "prettier", parser = "less", range = false }
 extensions = ["less"]
 line-comment = "//"
 block-comment = ["/*", "*/"]
diff --git a/languages/markdown.toml b/languages/markdown.toml
index 9fec38354..675ac34f3 100644
--- a/languages/markdown.toml
+++ b/languages/markdown.toml
@@ -1,5 +1,6 @@
 id = "markdown"
 name = "Markdown"
+formatter = { tool = "prettier", parser = "markdown", range = false }
 extensions = ["md", "markdown", "mdown", "mkd", "mkdn", "mdwn", "mdx", "ronn", "workbook"]
 block-comment = ["<!--", "-->"]
 indent = { tab-size = 2, insert-spaces = true }
diff --git a/languages/scss.toml b/languages/scss.toml
index 1fd1d0d5a..dcdaadd4c 100644
--- a/languages/scss.toml
+++ b/languages/scss.toml
@@ -1,5 +1,6 @@
 id = "scss"
 name = "SCSS"
+formatter = { tool = "prettier", parser = "scss", range = false }
 extensions = ["scss"]
 line-comment = "//"
 block-comment = ["/*", "*/"]
diff --git a/languages/typescript.toml b/languages/typescript.toml
index e5f231bc5..41817c5c3 100644
--- a/languages/typescript.toml
+++ b/languages/typescript.toml
@@ -1,5 +1,6 @@
 id = "typescript"
 name = "TypeScript"
+formatter = { tool = "prettier", parser = "typescript", range = true }
 extensions = ["ts", "mts", "cts"]
 line-comment = "//"
 block-comment = ["/*", "*/"]
diff --git a/languages/typescriptreact.toml b/languages/typescriptreact.toml
index 0a5069c7a..ad238c6c9 100644
--- a/languages/typescriptreact.toml
+++ b/languages/typescriptreact.toml
@@ -1,5 +1,6 @@
 id = "typescriptreact"
 name = "TypeScript JSX"
+formatter = { tool = "prettier", parser = "typescript", range = true }
 extensions = ["tsx"]
 line-comment = "//"
 block-comment = ["/*", "*/"]
diff --git a/languages/vue.toml b/languages/vue.toml
index a7cdade09..e260bce72 100644
--- a/languages/vue.toml
+++ b/languages/vue.toml
@@ -1,5 +1,6 @@
 id = "vue"
 name = "Vue"
+formatter = { tool = "prettier", parser = "vue", range = true }
 extensions = ["vue"]
 block-comment = ["<!--", "-->"]
 indent = { tab-size = 2, insert-spaces = true }
diff --git a/languages/yaml.toml b/languages/yaml.toml
index 76d550671..17e64e1b2 100644
--- a/languages/yaml.toml
+++ b/languages/yaml.toml
@@ -1,5 +1,6 @@
 id = "yaml"
 name = "YAML"
+formatter = { tool = "prettier", parser = "yaml", range = false }
 extensions = ["yaml", "yml"]
 filenames = [".clang-format", ".clang-tidy", ".clangd", ".gemrc", "pnpm-lock.yaml", "CITATION.cff"]
 first-line = "^%YAML"
diff --git a/plugins/kotlin-bridge/MANIFEST.MF b/plugins/kotlin-bridge/MANIFEST.MF
new file mode 100644
index 000000000..f0d3eebaa
--- /dev/null
+++ b/plugins/kotlin-bridge/MANIFEST.MF
@@ -0,0 +1,8 @@
+Manifest-Version: 1.0
+Bundle-ManifestVersion: 2
+Bundle-Name: OpenIDEA Kotlin binary bridge
+Bundle-SymbolicName: ai.openidea.kotlin;singleton:=true
+Bundle-Version: 1.0.0
+Bundle-RequiredExecutionEnvironment: JavaSE-21
+Require-Bundle: org.eclipse.jdt.ls.core,org.eclipse.jdt.core,
+ org.eclipse.core.runtime,org.eclipse.core.resources,com.google.gson
diff --git a/plugins/kotlin-bridge/README.md b/plugins/kotlin-bridge/README.md
new file mode 100644
index 000000000..a1eb4bf21
--- /dev/null
+++ b/plugins/kotlin-bridge/README.md
@@ -0,0 +1,73 @@
+# Kotlin binary bridge
+
+App-owned source, licensed under this repository's Apache-2.0 license. The jar
+contains no third-party implementation classes. JDT LS and Maven supply their
+respective APIs at runtime.
+
+`KotlinLibraries` is a JDT LS delegate command. `openidea.kotlin.replace` takes
+one complete array of `{projectUri, libraries: [{path, test}]}` objects and returns
+the number of changed projects. Paths name fully published, immutable directories.
+An empty array withdraws all owned libraries. Only library entries carrying
+`ai.openidea.kotlin=true` are removed; all other `IClasspathEntry` objects are
+retained, including containers, access rules, attributes and project references.
+A Java model listener restores the desired snapshot after Maven reimport.
+
+`IsolatedOutput` is a Java 8 Maven lifecycle participant, activated only in the
+private editor build via `-Dmaven.ext.class.path=<jar>` and
+`-Dopenidea.kotlin.staging=<absolute-directory>`. It redirects reactor output
+before lifecycle planning and records Maven's resolved dependency closure after
+each session, including failed builds. An execution listener records each module's
+Kotlin compile/test-compile targets as successful, failed or skipped. The host uses
+the project's Maven lifecycle/configuration,
+then publishes only classes whose actual `SourceFile` attribute ends in `.kt`,
+plus Kotlin module metadata. Java output is not bridged. Main/test Kotlin APIs and
+same-reactor consumers are covered; Precise Kotlin
+source navigation, unsaved analysis and refactoring are outside this bridge.
+
+The host debounces saved/source/configuration changes, cancels superseded process
+groups, and retains the last successful snapshot while rebuilding. Maven runs
+with `--fail-at-end`. A new snapshot is attached only when all Kotlin targets in
+modules containing Kotlin sources succeed, even if javac fails. Java diagnostics
+belong to JDT. Failed or skipped Kotlin targets retain the previous snapshot and
+report errors under `kotlin-bridge` Problems and a notification explaining the
+older API. Old directories are deleted only after JDT acknowledges replacement.
+With no Kotlin sources left, all managed libraries and bridge diagnostics are
+withdrawn, even when the POM still declares the Kotlin plugin. Extensionless
+watcher paths trigger only below a Maven module's `src/`, outside generated and
+user-excluded directories. Run/Debug preparation is independent of this editor
+build.
+
+## Build
+
+Built against JDT LS 1.63.0 and Maven 3.9.11, using their installed API jars.
+`build-dependencies.sha256` pins all build inputs. The build refuses different
+inputs; `--record-dependencies` is an explicit maintainer action when updating
+those dependencies. Compilation uses the JDT batch compiler with Java 21 target
+for the JDT command and Java 8 target for the Maven participant. Use Java 25 to
+run the build compiler. Archive order and timestamps are deterministic.
+
+```sh
+python3 plugins/kotlin-bridge/build.py /path/to/jdtls /path/to/maven
+shasum -a 256 plugins/kotlin-bridge/openidea-kotlin-bridge.jar
+```
+
+Committed jar SHA-256:
+`5c6407a85bd3cfcde0ee68b2f223dd3d1ca0e5165ff76a2249191617496b1fcd`.
+
+The SDK embeds this jar with `include_bytes!`, writes it atomically into the app
+data directory, and includes it in JDT LS initialization bundles.
+
+## Integration regression
+
+```sh
+# `java` on PATH must satisfy JDT LS; JAVA_HOME selects Maven's project JDK.
+JAVA_HOME=/path/to/project/jdk python3 plugins/kotlin-bridge/tests/verify.py /path/to/jdtls
+```
+
+Requires Maven on PATH and access to Kotlin 2.0.10 and the fixture's Maven
+plugins (or their existing local cache). The test creates its own projects,
+workspace, bundle copy and JDT process. It checks baseline errors, single/reactor
+resolution, SMS/member completion, binary definition locations, preservation of
+unowned entries, reimport, API changes, publication despite javac failure,
+failed/skipped Kotlin target retention, deletion withdrawal and repair. Evidence
+and protocol transcripts are written to a printed temporary directory. Only the spawned JDT process is terminated.
diff --git a/plugins/kotlin-bridge/build-dependencies.sha256 b/plugins/kotlin-bridge/build-dependencies.sha256
new file mode 100644
index 000000000..23592d907
--- /dev/null
+++ b/plugins/kotlin-bridge/build-dependencies.sha256
@@ -0,0 +1,161 @@
+beebede8db065fe1b72909ecc66bb49acda618901635d86c25fce14a5915e37e  jdt/ch.qos.logback.classic_1.6.3.jar
+a6967a28c8b086dee75a694d2f6fb8830c71153539866d7d8af065c9b6df91e0  jdt/ch.qos.logback.core_1.6.3.jar
+2cbd119bf1961c28788310963dc80ba65f58cdeec1dd139c8bdb1240faa2c36f  jdt/com.google.gson_2.14.0.jar
+cbfc3906b19b8f55dd7cfd6dfe0aa4532e834250d7f080bd8d211a3e246b59cb  jdt/com.google.guava.failureaccess_1.0.3.jar
+796d8e28ac64e83a47c4c5935a8fecc4682650a04bbdead738ef0f5a3a0e6c46  jdt/com.google.guava_33.7.1.jre.jar
+3b3864f5b449e9c3c24b16861524b622b086563f44e0cd8384c8efc5a6052f82  jdt/com.sun.jna.platform_5.19.1.jar
+467b2990d4f406e7d41f7a989f89df257767ca11d566f844560e2ab8d09f6433  jdt/com.sun.jna_5.19.1.v20260612-1000.jar
+85fb03fc054cdf4efca8efd9b6712bbb418e1ab98241c4539c8585bbc23e1b8a  jdt/jakarta.annotation-api_1.3.5.jar
+a852b0971c589491e24334bd77e92760c048d2c102fc4c68e582e1cd53130f84  jdt/jakarta.inject.jakarta.inject-api_1.0.5.jar
+2506fb25a748d4a5e5ec549d8bb063889d0f213e9cfbd6fd6fcbdc93b4f35bbb  jdt/jakarta.servlet-api_6.2.0.M2.jar
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+8f7f8605d68e15bf32db61ec94eac6fdafc51b1bdbe1e0e0802b57d23f387792  jdt/org.apache.commons.cli_1.11.0.jar
+78a5d732fbd715e2d10bd7150d2f8030bae57267f8aacc5c88f642cb6c2e5d3f  jdt/org.apache.commons.commons-codec_1.22.1.jar
+69e5c9fa35da7a51a5fd2099dfe56a2d8d32cf233e2f6d770e796146440263f4  jdt/org.apache.commons.lang3_3.20.0.jar
+c5bd887c8fd5ec4cd563249e7552bb1a1a1ca57e05a1f1ef8425a7b7b7bd2fbe  jdt/org.apache.felix.scr_2.2.18.jar
+c375b6d5b71efe179e5763a6d83fcf10e303c0bf82031310a46769727ac90da0  jdt/org.commonmark.ext-gfm-tables_0.30.1.jar
+9b0d20064975a17e876fcb4b599c6b3667f46a7739ed61e2f06c96f44b50629f  jdt/org.commonmark_0.30.1.jar
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+e75b07863128a076989d15e815d63a49cab772a338f1f0444d007bef3fa94601  jdt/org.eclipse.compare.core_3.8.900.v20260731-0809.jar
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+941b3c5feeba4ec0a949a8a94ff10283b2505813fa736c9e6345f146ae1b7e8a  jdt/org.eclipse.core.jobs_3.15.900.v20260604-0622.jar
+6e7a8db7d87a44bb35924bb345ddf0d9372413e3fee2edd842b50ed630ec254f  jdt/org.eclipse.core.net_1.5.900.v20260507-0401.jar
+e22d47e2e68713a74bfacd134dc01b1aa904a1b429769241483e058de166acea  jdt/org.eclipse.core.resources_3.25.0.v20261010-1447.jar
+0947f29f5c5b7d234e3b735de2d00d33ae6e3ee428a61bb818f9c0fe2b809735  jdt/org.eclipse.core.runtime_3.35.100.v20260910-1515.jar
+553f09a59f2662fa4a3bbc94e84bd83221c1c6fb532d81b57010162fb47460a6  jdt/org.eclipse.core.variables_3.6.900.v20260602-0702.jar
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+fd353398835107608f554779a6e91891725efb94e0f57559d0ab3cea4b6156c7  jdt/org.eclipse.equinox.app_1.7.600.v20251211-1038.jar
+28749ec64dac9d0e20e00becc3d5f9daccb5637455c9c546ab07be324011ef84  jdt/org.eclipse.equinox.common_3.21.100.v20260829-1451.jar
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+d3ef575e3e4979678dc01bf1dcce51021493b4d11fb7f1be8ad982877c16a1c0  maven/slf4j-api-1.7.36.jar
+afc9216fa97b78dad227b4a8d4d67b9897bf113a57f80598d62993841113e103  maven/wagon-file-3.5.3.jar
+d2b6e48c9fcbe579e1858c622d14464011ff265fa6e28e794004a6882154a509  maven/wagon-http-3.5.3.jar
+8e7da766f55164fde8779aaaa125832506c2848cab4876b5305138873e28037f  maven/wagon-http-shared-3.5.3.jar
+5e72000338945ed3e96f8e4f578d1d0672e1af7e19c0e9014197ae5b31af3ef4  maven/wagon-provider-api-3.5.3.jar
diff --git a/plugins/kotlin-bridge/build.py b/plugins/kotlin-bridge/build.py
new file mode 100644
index 000000000..538b749c3
--- /dev/null
+++ b/plugins/kotlin-bridge/build.py
@@ -0,0 +1,32 @@
+"""Build with JDT LS 1.63.0 + Maven 3.9.11. Checksums pin every compiler dependency."""
+import hashlib
+import os
+import pathlib
+import subprocess
+import sys
+import tempfile
+import zipfile
+
+root = pathlib.Path(__file__).resolve().parent
+jdt, maven = map(lambda p: pathlib.Path(p).resolve(), sys.argv[1:3])
+jars = sorted((jdt / 'plugins').glob('*.jar')) + sorted((maven / 'lib').glob('*.jar'))
+actual = ''.join(f'{hashlib.sha256(p.read_bytes()).hexdigest()}  {"jdt/" if p.parent.name == "plugins" else "maven/"}{p.name}\n' for p in jars)
+if '--record-dependencies' in sys.argv:
+    (root / 'build-dependencies.sha256').write_text(actual)
+if (root / 'build-dependencies.sha256').read_text() != actual:
+    sys.exit('Build dependencies differ from build-dependencies.sha256')
+with tempfile.TemporaryDirectory() as output:
+    for source, target, classpath in [('src', '-21', jars[:len(list((jdt / 'plugins').glob('*.jar')))]), ('maven', '-8', jars)]:
+        subprocess.run(['java', '-cp', str(jdt / 'plugins/*'), 'org.eclipse.jdt.internal.compiler.batch.Main', target, '-proc:none', '-classpath', os.pathsep.join(map(str, classpath)), '-d', output, *map(str, sorted((root/source).rglob('*.java')))], check=True)
+    files = {'META-INF/MANIFEST.MF': root/'MANIFEST.MF', 'plugin.xml': root/'plugin.xml', 'META-INF/plexus/components.xml': root/'components.xml'}
+    files.update({p.relative_to(output).as_posix(): p for p in pathlib.Path(output).rglob('*.class')})
+    archive = pathlib.Path(output)/'bundle.jar'
+    with zipfile.ZipFile(archive, 'w', zipfile.ZIP_DEFLATED) as jar:
+        for name, path in sorted(files.items()):
+            data = path.read_bytes()
+            if name == 'META-INF/MANIFEST.MF':
+                data = data.rstrip(b'\r\n') + b'\n\n'
+            jar.writestr(zipfile.ZipInfo(name, (2026, 1, 1, 0, 0, 0)), data)
+    staged = root/'openidea-kotlin-bridge.jar.pending'
+    staged.write_bytes(archive.read_bytes())
+    staged.replace(root/'openidea-kotlin-bridge.jar')
diff --git a/plugins/kotlin-bridge/components.xml b/plugins/kotlin-bridge/components.xml
new file mode 100644
index 000000000..156cd7d36
--- /dev/null
+++ b/plugins/kotlin-bridge/components.xml
@@ -0,0 +1,5 @@
+<component-set><components><component>
+  <role>org.apache.maven.AbstractMavenLifecycleParticipant</role>
+  <role-hint>openidea-kotlin-output</role-hint>
+  <implementation>ai.openidea.kotlin.IsolatedOutput</implementation>
+</component></components></component-set>
diff --git a/plugins/kotlin-bridge/maven/ai/openidea/kotlin/IsolatedOutput.java b/plugins/kotlin-bridge/maven/ai/openidea/kotlin/IsolatedOutput.java
new file mode 100644
index 000000000..8da379947
--- /dev/null
+++ b/plugins/kotlin-bridge/maven/ai/openidea/kotlin/IsolatedOutput.java
@@ -0,0 +1,177 @@
+package ai.openidea.kotlin;
+
+import java.io.*;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.*;
+import java.util.*;
+import org.apache.maven.AbstractMavenLifecycleParticipant;
+import org.apache.maven.artifact.Artifact;
+import org.apache.maven.MavenExecutionException;
+import org.apache.maven.execution.*;
+import java.lang.reflect.*;
+import org.apache.maven.model.*;
+import org.apache.maven.project.MavenProject;
+import org.codehaus.plexus.util.xml.Xpp3Dom;
+
+/** Loaded only by the private bridge build, before lifecycle plans are calculated. */
+public final class IsolatedOutput extends AbstractMavenLifecycleParticipant {
+    private final Map<MavenProject, File> outputs = new LinkedHashMap<>();
+    private File staging;
+    private final Map<MavenProject, Map<String, String>> kotlin = new LinkedHashMap<>();
+    private final Set<MavenProject> sources = new HashSet<>();
+
+    @Override public void afterProjectsRead(MavenSession session) throws MavenExecutionException {
+        String destination = session.getUserProperties().getProperty("openidea.kotlin.staging");
+        if (destination == null) throw new MavenExecutionException("Missing Kotlin staging directory", (File) null);
+        staging = new File(destination);
+        int index = 0;
+        for (MavenProject project : session.getProjects()) {
+            File build = new File(staging, Integer.toString(index++));
+            File main = new File(build, "classes");
+            File test = new File(build, "test-classes");
+            project.getBuild().setDirectory(build.getAbsolutePath());
+            project.getBuild().setOutputDirectory(main.getAbsolutePath());
+            project.getBuild().setTestOutputDirectory(test.getAbsolutePath());
+            for (Plugin plugin : project.getBuildPlugins()) {
+                if ("kotlin-maven-plugin".equals(plugin.getArtifactId())) {
+                    plugin.setConfiguration(redirect(plugin.getConfiguration(), build, main, test));
+                    for (PluginExecution execution : plugin.getExecutions())
+                        execution.setConfiguration(redirect(execution.getConfiguration(), build, main, test));
+                } else if ("maven-compiler-plugin".equals(plugin.getArtifactId())) {
+                    plugin.setConfiguration(compiler(plugin.getConfiguration()));
+                    for (PluginExecution execution : plugin.getExecutions())
+                        execution.setConfiguration(compiler(execution.getConfiguration()));
+                }
+            }
+            outputs.put(project, main);
+            Map<String, String> goals = new LinkedHashMap<>();
+            for (Plugin plugin : project.getBuildPlugins()) {
+                if (!isKotlin(plugin)) continue;
+                for (PluginExecution execution : plugin.getExecutions()) {
+                    if ("none".equals(execution.getPhase())) continue;
+                    for (String goal : execution.getGoals())
+                        if ("compile".equals(goal) || "test-compile".equals(goal))
+                            goals.put(execution.getId() + ":" + goal, "skipped");
+                }
+            }
+            kotlin.put(project, goals);
+            if (hasKotlin(project.getBasedir().toPath(), project.getBasedir().toPath(), session.getProjects()))
+                sources.add(project);
+        }
+        final ExecutionListener previous = session.getRequest().getExecutionListener();
+        // Preserve Maven's logger and any listener installed by another extension.
+        session.getRequest().setExecutionListener((ExecutionListener) Proxy.newProxyInstance(
+            ExecutionListener.class.getClassLoader(), new Class<?>[] { ExecutionListener.class },
+            (proxy, method, args) -> {
+                if (args != null && args.length == 1 && args[0] instanceof ExecutionEvent) {
+                    ExecutionEvent event = (ExecutionEvent) args[0];
+                    if (Arrays.asList("mojoStarted", "mojoSucceeded", "mojoFailed", "mojoSkipped").contains(method.getName())
+                        && event.getMojoExecution() != null && isKotlin(event.getMojoExecution().getPlugin())) {
+                        String goal = event.getMojoExecution().getGoal();
+                        if ("compile".equals(goal) || "test-compile".equals(goal)) {
+                            String status = method.getName().equals("mojoSucceeded") ? "success" :
+                                method.getName().equals("mojoFailed") ? "failed" : "skipped";
+                            Map<String, String> goals = kotlin.get(event.getProject());
+                            if (goals != null) goals.put(event.getMojoExecution().getExecutionId() + ":" + goal, status);
+                        }
+                    }
+                }
+                if (previous == null) return null;
+                try { return method.invoke(previous, args); }
+                catch (InvocationTargetException e) { throw e.getCause(); }
+            }));
+    }
+
+    private static boolean isKotlin(Plugin plugin) {
+        return "org.jetbrains.kotlin".equals(plugin.getGroupId()) && "kotlin-maven-plugin".equals(plugin.getArtifactId());
+    }
+    private static boolean hasKotlin(Path root, Path directory, List<MavenProject> projects) throws MavenExecutionException {
+        if (!directory.equals(root)) {
+            String name = directory.getFileName().toString();
+            if (Arrays.asList("target", "build", "out", "bin", ".git", "node_modules", ".openidea").contains(name)) return false;
+            for (MavenProject project : projects) if (project.getBasedir().toPath().equals(directory)) return false;
+        }
+        if (!Files.isDirectory(directory, LinkOption.NOFOLLOW_LINKS)) return false;
+        try (DirectoryStream<Path> entries = Files.newDirectoryStream(directory)) {
+            for (Path path : entries) {
+                if (Files.isRegularFile(path, LinkOption.NOFOLLOW_LINKS) && path.toString().endsWith(".kt")) return true;
+                if (hasKotlin(root, path, projects)) return true;
+            }
+            return false;
+        } catch (IOException e) { throw new MavenExecutionException("Cannot inspect Kotlin sources", e); }
+    }
+
+    @Override public void afterSessionEnd(MavenSession session) throws MavenExecutionException {
+        if (staging == null) return;
+        List<String> modules = new ArrayList<>();
+        for (Map.Entry<MavenProject, File> entry : outputs.entrySet()) {
+            MavenProject project = entry.getKey();
+            File main = entry.getValue();
+            List<String> dependencies = new ArrayList<>();
+            // Maven has applied dependency management, mediation, scopes, optional
+            // propagation and exclusions. Do not reconstruct that graph from POMs.
+            for (Artifact dependency : project.getArtifacts()) {
+                dependencies.add("{\"key\":" + quote(dependency.getGroupId() + ":" + dependency.getArtifactId() + ":" + dependency.getVersion()) +
+                    ",\"scope\":" + quote(dependency.getScope() == null ? "compile" : dependency.getScope()) +
+                    ",\"optional\":" + dependency.isOptional() + ",\"type\":" + quote(dependency.getType()) +
+                    ",\"classifier\":" + quote(dependency.getClassifier()) + "}");
+            }
+            List<String> goals = new ArrayList<>();
+            for (Map.Entry<String, String> goal : kotlin.get(project).entrySet())
+                goals.add("{\"execution\":" + quote(goal.getKey()) + ",\"status\":" + quote(goal.getValue()) + "}");
+            modules.add("{\"key\":" + quote(project.getGroupId() + ":" + project.getArtifactId() + ":" + project.getVersion()) +
+                ",\"projectUri\":" + quote(project.getBasedir().toURI().toString()) +
+                ",\"output\":" + quote(main.getAbsolutePath()) +
+                ",\"testOutput\":" + quote(project.getBuild().getTestOutputDirectory()) +
+                ",\"hasKotlin\":" + sources.contains(project) +
+                ",\"kotlinGoals\":[" + String.join(",", goals) + "]" +
+                ",\"dependencies\":[" + String.join(",", dependencies) + "]}");
+        }
+        try {
+            Files.createDirectories(staging.toPath());
+            Files.write(new File(staging.getParentFile(), "modules.json").toPath(),
+                ("[" + String.join(",", modules) + "]").getBytes(StandardCharsets.UTF_8));
+        } catch (IOException e) {
+            throw new MavenExecutionException("Cannot write Kotlin module manifest", e);
+        }
+    }
+
+    private static Xpp3Dom config(Object value) {
+        return value instanceof Xpp3Dom ? new Xpp3Dom((Xpp3Dom) value) : new Xpp3Dom("configuration");
+    }
+    private static void set(Xpp3Dom config, String name, File path) {
+        Xpp3Dom child = config.getChild(name);
+        if (child == null) { child = new Xpp3Dom(name); config.addChild(child); }
+        child.setValue(path.getAbsolutePath());
+    }
+    private static Xpp3Dom redirect(Object value, File build, File main, File test) {
+        Xpp3Dom config = config(value);
+        set(config, "output", main);
+        set(config, "testOutput", test);
+        set(config, "incrementalCachesRoot", new File(build, "kotlin-ic"));
+        Xpp3Dom incremental = config.getChild("myIncremental");
+        if (incremental == null) { incremental = new Xpp3Dom("myIncremental"); config.addChild(incremental); }
+        incremental.setValue("false");
+        return config;
+    }
+    private static Xpp3Dom compiler(Object value) {
+        Xpp3Dom config = config(value);
+        // compile and testCompile share the parameter name outputDirectory but
+        // have different defaults. Let each mojo read the redirected build model.
+        for (int i = config.getChildCount() - 1; i >= 0; i--) {
+            String name = config.getChild(i).getName();
+            if ("outputDirectory".equals(name) || "testOutputDirectory".equals(name)) config.removeChild(i);
+        }
+        return config;
+    }
+    private static String quote(String text) {
+        if (text == null) return "null";
+        StringBuilder out = new StringBuilder("\"");
+        for (char c : text.toCharArray()) {
+            if (c == '\\' || c == '"') out.append('\\').append(c);
+            else if (c < 32) out.append(String.format("\\u%04x", (int) c));
+            else out.append(c);
+        }
+        return out.append('"').toString();
+    }
+}
diff --git a/plugins/kotlin-bridge/openidea-kotlin-bridge.jar b/plugins/kotlin-bridge/openidea-kotlin-bridge.jar
new file mode 100644
index 000000000..8250780f3
Binary files /dev/null and b/plugins/kotlin-bridge/openidea-kotlin-bridge.jar differ
diff --git a/plugins/kotlin-bridge/plugin.xml b/plugins/kotlin-bridge/plugin.xml
new file mode 100644
index 000000000..a0ac23ef7
--- /dev/null
+++ b/plugins/kotlin-bridge/plugin.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<plugin>
+  <extension point="org.eclipse.jdt.ls.core.delegateCommandHandler">
+    <delegateCommandHandler class="ai.openidea.kotlin.KotlinLibraries">
+      <command id="openidea.kotlin.replace"/>
+    </delegateCommandHandler>
+  </extension>
+</plugin>
diff --git a/plugins/kotlin-bridge/src/ai/openidea/kotlin/KotlinLibraries.java b/plugins/kotlin-bridge/src/ai/openidea/kotlin/KotlinLibraries.java
new file mode 100644
index 000000000..8f92e7efd
--- /dev/null
+++ b/plugins/kotlin-bridge/src/ai/openidea/kotlin/KotlinLibraries.java
@@ -0,0 +1,94 @@
+package ai.openidea.kotlin;
+
+import com.google.gson.Gson;
+import java.io.File;
+import java.net.URI;
+import java.util.*;
+import org.eclipse.core.resources.ResourcesPlugin;
+import org.eclipse.core.runtime.*;
+import org.eclipse.core.runtime.jobs.Job;
+import org.eclipse.jdt.core.*;
+import org.eclipse.jdt.ls.core.internal.IDelegateCommandHandler;
+
+/** Owns only marked binary entries; Maven and user entries retain their identities. */
+public final class KotlinLibraries implements IDelegateCommandHandler {
+    private static final String OWNER = "ai.openidea.kotlin";
+    private static final Object LOCK = new Object();
+    private static List<ProjectLibraries> desired = List.of();
+    private static boolean listening;
+    private static final Job reconcileJob = new Job("Kotlin binary libraries") {
+        @Override protected IStatus run(IProgressMonitor monitor) {
+            synchronized (LOCK) {
+                try {
+                    reconcile(monitor);
+                    return Status.OK_STATUS;
+                } catch (CoreException e) {
+                    return e.getStatus();
+                }
+            }
+        }
+    };
+    private static class Library { String path; boolean test; }
+    private static class ProjectLibraries { String projectUri; List<Library> libraries; }
+
+    @Override public Object executeCommand(String command, List<Object> arguments, IProgressMonitor monitor) throws Exception {
+        if (!"openidea.kotlin.replace".equals(command) || arguments.size() != 1)
+            throw new IllegalArgumentException("Expected one Kotlin library snapshot");
+        Gson gson = new Gson();
+        ProjectLibraries[] snapshot = gson.fromJson(gson.toJson(arguments.get(0)), ProjectLibraries[].class);
+        for (ProjectLibraries project : snapshot) {
+            new File(URI.create(project.projectUri));
+            for (Library library : project.libraries) {
+                if (!new File(library.path).isAbsolute() || !new File(library.path).isDirectory())
+                    throw new IllegalArgumentException("Kotlin library must be a published directory: " + library.path);
+            }
+        }
+        synchronized (LOCK) {
+            if (monitor.isCanceled()) throw new OperationCanceledException();
+            desired = List.of(snapshot);
+            if (!listening) {
+                JavaCore.addElementChangedListener(event -> reconcileJob.schedule(200), ElementChangedEvent.POST_CHANGE);
+                listening = true;
+            }
+            return reconcile(monitor);
+        }
+    }
+
+    private static File canonical(URI uri) {
+        File file = new File(uri);
+        try { return file.getCanonicalFile(); }
+        catch (java.io.IOException e) { return file.getAbsoluteFile(); }
+    }
+
+    private static int reconcile(IProgressMonitor monitor) throws CoreException {
+        int changed = 0;
+        for (IJavaProject project : JavaCore.create(ResourcesPlugin.getWorkspace().getRoot()).getJavaProjects()) {
+            if (!project.getProject().isAccessible()) continue;
+            List<IClasspathEntry> entries = new ArrayList<>();
+            IClasspathEntry[] original = project.getRawClasspath();
+            for (IClasspathEntry entry : original) {
+                boolean owned = entry.getEntryKind() == IClasspathEntry.CPE_LIBRARY &&
+                    Arrays.stream(entry.getExtraAttributes()).anyMatch(a -> OWNER.equals(a.getName()) && "true".equals(a.getValue()));
+                if (!owned) entries.add(entry);
+            }
+            URI location = project.getProject().getLocationURI();
+            for (ProjectLibraries item : desired) {
+                if (location == null || !canonical(location).equals(canonical(URI.create(item.projectUri)))) continue;
+                for (Library library : item.libraries) {
+                    List<IClasspathAttribute> attributes = new ArrayList<>();
+                    attributes.add(JavaCore.newClasspathAttribute(OWNER, "true"));
+                    if (library.test) attributes.add(JavaCore.newClasspathAttribute(IClasspathAttribute.TEST, "true"));
+                    entries.add(JavaCore.newLibraryEntry(Path.fromOSString(library.path), null, null,
+                        new IAccessRule[0], attributes.toArray(IClasspathAttribute[]::new), false));
+                }
+            }
+            IClasspathEntry[] updated = entries.toArray(IClasspathEntry[]::new);
+            if (!Arrays.equals(original, updated)) {
+                if (monitor.isCanceled()) throw new OperationCanceledException();
+                project.setRawClasspath(updated, monitor);
+                changed++;
+            }
+        }
+        return changed;
+    }
+}
diff --git a/plugins/kotlin-bridge/tests/verify.py b/plugins/kotlin-bridge/tests/verify.py
new file mode 100644
index 000000000..3d6c89862
--- /dev/null
+++ b/plugins/kotlin-bridge/tests/verify.py
@@ -0,0 +1,275 @@
+"""Real Maven + JDT LS regression: python3 verify.py JDT_HOME (Java 25; Maven uses JAVA_HOME)."""
+import json
+import os
+import pathlib
+import platform
+import queue
+import shutil
+import subprocess
+import sys
+import tempfile
+import threading
+import time
+import xml.etree.ElementTree as ET
+
+home = pathlib.Path(sys.argv[1]).resolve()
+bundle = pathlib.Path(__file__).resolve().parents[1] / 'openidea-kotlin-bridge.jar'
+work = pathlib.Path(tempfile.mkdtemp(prefix='openidea-kotlin-bridge-', dir=os.environ.get('TMPDIR'))).resolve()
+copied_bundle = work/'openidea-kotlin-bridge.jar'
+shutil.copyfile(bundle, copied_bundle)
+bundle = copied_bundle
+projects = work / 'projects'
+single = projects / 'single'
+multi = projects / 'multi'
+lib = multi / 'channel-lib'
+app = multi / 'app'
+for directory in [single, lib, app]:
+    (directory / 'src/main/java/probe').mkdir(parents=True)
+plugin = '''<build><plugins><plugin><groupId>org.jetbrains.kotlin</groupId><artifactId>kotlin-maven-plugin</artifactId><version>2.0.10</version><executions><execution><id>kotlin-compile</id><phase>process-sources</phase><goals><goal>compile</goal></goals><configuration><jvmTarget>1.8</jvmTarget><sourceDirs><sourceDir>src/main/java</sourceDir></sourceDirs></configuration></execution></executions></plugin><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-compiler-plugin</artifactId><version>3.13.0</version></plugin></plugins></build>'''
+plugin = plugin.replace('</executions>', '<execution><id>kotlin-test</id><phase>process-test-sources</phase><goals><goal>test-compile</goal></goals><configuration><jvmTarget>1.8</jvmTarget><sourceDirs><sourceDir>src/test/java</sourceDir></sourceDirs></configuration></execution></executions>')
+stdlib = '<dependencies><dependency><groupId>org.jetbrains.kotlin</groupId><artifactId>kotlin-stdlib</artifactId><version>2.0.10</version></dependency></dependencies>'
+properties = '<properties><maven.compiler.source>8</maven.compiler.source><maven.compiler.target>8</maven.compiler.target></properties>'
+prefix = '<project xmlns="http://maven.apache.org/POM/4.0.0"><modelVersion>4.0.0</modelVersion>'
+(single / 'pom.xml').write_text(prefix + '<groupId>probe</groupId><artifactId>single</artifactId><version>1</version>' + properties + stdlib + plugin + '</project>')
+(multi / 'pom.xml').write_text(prefix + '<groupId>probe</groupId><artifactId>reactor</artifactId><version>1</version><packaging>pom</packaging>' + properties + '<modules><module>channel-lib</module><module>app</module></modules></project>')
+parent = '<parent><groupId>probe</groupId><artifactId>reactor</artifactId><version>1</version></parent>'
+(lib / 'pom.xml').write_text(prefix + parent + '<artifactId>channel-lib</artifactId>' + stdlib + plugin + '</project>')
+(app / 'pom.xml').write_text(prefix + parent + '<artifactId>app</artifactId><dependencies><dependency><groupId>probe</groupId><artifactId>channel-lib</artifactId><version>1</version></dependency></dependencies></project>')
+source = 'package probe;\npublic class Caller {\n    public Channel channel() {\n        return Channel.SMS;\n    }\n}\n'
+for directory in [single, app]:
+    (directory / 'src/main/java/probe/Caller.java').write_text(source)
+for directory in [single, lib]:
+    (directory / 'src/main/java/probe/Channel.kt').write_text('package probe\nenum class Channel { SMS }\n')
+
+(single/'src/test/java/probe').mkdir(parents=True)
+test_source = source.replace('Caller', 'TestCaller').replace('Channel', 'TestChannel')
+(single/'src/test/java/probe/TestCaller.java').write_text(test_source)
+(single/'src/test/java/probe/TestChannel.kt').write_text('package probe\nenum class TestChannel { SMS }\n')
+
+config = work / 'config'
+config.mkdir()
+base = {'Darwin': 'config_mac', 'Windows': 'config_win'}.get(platform.system(), 'config_linux')
+names = [base + '_arm', base] if platform.machine().lower() in ('arm64', 'aarch64') else [base]
+shutil.copyfile(next(home / n / 'config.ini' for n in names if (home/n/'config.ini').exists()), config/'config.ini')
+proc = subprocess.Popen(['java', '-Declipse.application=org.eclipse.jdt.ls.core.id1', '-Dosgi.bundles.defaultStartLevel=4', '-Declipse.product=org.eclipse.jdt.ls.core.product', '-Xmx1G', '--add-modules=ALL-SYSTEM', '--add-opens', 'java.base/java.util=ALL-UNNAMED', '--add-opens', 'java.base/java.lang=ALL-UNNAMED', '-jar', str(next((home/'plugins').glob('org.eclipse.equinox.launcher_*.jar'))), '-configuration', str(config), '-data', str(work/'metadata')], stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=(work/'stderr.log').open('w'))
+messages = queue.Queue()
+lock = threading.Lock()
+transcript = []
+seq = 0
+def send(message):
+    data = json.dumps({'jsonrpc': '2.0', **message}).encode()
+    with lock:
+        proc.stdin.write(f'Content-Length: {len(data)}\r\n\r\n'.encode() + data)
+        proc.stdin.flush()
+def read():
+    while True:
+        headers = {}
+        while True:
+            line = proc.stdout.readline()
+            if not line: return
+            if line == b'\r\n': break
+            key, value = line.decode().split(':', 1)
+            headers[key.lower()] = value.strip()
+        message = json.loads(proc.stdout.read(int(headers['content-length'])))
+        if 'method' in message and 'id' in message:
+            send({'id':message['id'], 'result': [] if message['method']=='workspace/configuration' else None})
+        else:
+            messages.put(message)
+threading.Thread(target=read, daemon=True).start()
+def request(method, params):
+    global seq
+    seq += 1
+    send({'id':seq, 'method':method, 'params':params})
+    deadline = time.monotonic() + 240
+    while time.monotonic() < deadline:
+        message = messages.get(timeout=max(1, deadline-time.monotonic()))
+        transcript.append(message)
+        if message.get('id') == seq:
+            if 'error' in message: raise RuntimeError(message['error'])
+            return message.get('result')
+    raise TimeoutError(method)
+def command(snapshot):
+    response = request('workspace/executeCommand', {'command':'openidea.kotlin.replace', 'arguments':[snapshot]})
+    assert isinstance(response, (int, float)), response
+    return response
+def build(directory, revision, expected=True):
+    staging = work / revision
+    result = subprocess.run(['mvn', '-B', '-fae', '-Dstyle.color=never', f'-Dmaven.ext.class.path={bundle}', f'-Dopenidea.kotlin.staging={staging}/staging', 'test-compile'], cwd=directory, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
+    (work/f'{revision}.log').write_bytes(result.stdout)
+    modules = json.loads((staging/'modules.json').read_text())
+    eligible = all(m['kotlinGoals'] and all(g['status'] == 'success' for g in m['kotlinGoals']) for m in modules if m['hasKotlin'])
+    assert eligible == expected, (modules, result.stdout.decode())
+    evidence[revision + '-build'] = {'exitCode':result.returncode, 'modules':modules, 'eligible':eligible}
+    return modules
+def library(module, revision, test=False, name="Channel"):
+    directory = work/'published'/revision
+    directory.mkdir(parents=True)
+    output = module['testOutput' if test else 'output']
+    for file in pathlib.Path(output).rglob('TestChannel*.class' if test else name+'*.class'):
+        destination = directory/file.relative_to(output)
+        destination.parent.mkdir(parents=True, exist_ok=True)
+        shutil.copyfile(file, destination)
+    assert list(directory.rglob('*.class')), module
+    return {'path':str(directory), 'test':test}
+def state(directory, label, expected, test=False):
+    file = directory/('src/test/java/probe/TestCaller.java' if test else 'src/main/java/probe/Caller.java')
+    deadline = time.monotonic() + 30
+    while True:
+        time.sleep(0.25)
+        request('workspace/symbol', {'query':'Caller'})
+        reports = [m['params'] for m in transcript if m.get('method')=='textDocument/publishDiagnostics' and m['params']['uri']==file.as_uri()]
+        errors = [d for d in reports[-1]['diagnostics'] if d.get('severity')==1] if reports else None
+        if errors is not None and ((errors == []) == expected): break
+        if time.monotonic() > deadline: raise AssertionError((label, errors))
+    completion = request('textDocument/completion', {'textDocument':{'uri':file.as_uri()}, 'position':{'line':3,'character':27 if test else 23}})
+    items = completion.get('items', []) if isinstance(completion, dict) else completion or []
+    labels = [item['label'] for item in items]
+    definition = request('textDocument/definition', {'textDocument':{'uri':file.as_uri()}, 'position':{'line':2,'character':12}})
+    result = {'errors':errors, 'completion':labels, 'definition':definition}
+    evidence[label] = result
+    assert errors is not None, (label, "no published diagnostics")
+    assert (errors == []) == expected, (label, errors)
+    assert any(label.startswith('SMS') for label in labels) == expected, (label, labels)
+    assert bool(definition) == expected, (label, definition)
+    if expected:
+        location = definition[0]
+        assert location.get('uri', location.get('targetUri', '')).startswith('jdt:'), definition
+    return result
+
+evidence = {'work':str(work)}
+try:
+    init = request('initialize', {'processId':None, 'rootUri':projects.as_uri(), 'workspaceFolders':[{'uri':projects.as_uri(), 'name':'projects'}], 'capabilities':{'textDocument':{'completion':{'completionItem':{'snippetSupport':True}}, 'definition':{'linkSupport':True}}}, 'initializationOptions':{'bundles':[str(bundle)], 'extendedClientCapabilities':{'classFileContentsSupport':True}, 'settings':{'java':{'import':{'gradle':{'enabled':False}, 'maven':{'enabled':True}}, 'configuration':{'updateBuildConfiguration':'automatic'}}}}})
+    send({'method':'initialized', 'params':{}})
+    request('java/buildWorkspace', True)
+    for directory, test in [(single,False), (app,False), (single,True)]:
+        file = directory/('src/test/java/probe/TestCaller.java' if test else 'src/main/java/probe/Caller.java')
+        send({'method':'textDocument/didOpen','params':{'textDocument':{'uri':file.as_uri(),'languageId':'java','version':1,'text':test_source if test else source}}})
+    # Allow reconcile jobs to publish their first marker batch.
+    time.sleep(2)
+    state(single, 'single-before', False)
+    state(app, 'multi-before', False)
+    state(single, 'test-before', False, True)
+    def raw(directory):
+        entries = ET.parse(directory/'.classpath').getroot()
+        return [ET.tostring(e).decode().strip() for e in entries if not any(a.get('name')=='ai.openidea.kotlin' for a in e.findall('./attributes/attribute'))]
+    before = {str(d):raw(d) for d in [single, lib, app]}
+    sm = build(single, 'single-build')[0]
+    assert not (pathlib.Path(sm['output'])/'probe/TestCaller.class').exists()
+    assert (pathlib.Path(sm['testOutput'])/'probe/TestCaller.class').is_file()
+    mm = build(multi, 'multi-build')
+    lm = next(m for m in mm if 'channel-lib' in m['key'])
+    sl, ml = library(sm, 'single'), library(lm, 'multi')
+    snapshot = [{'projectUri':single.as_uri(),'libraries':[sl, library(sm, 'single-test', True)]}, {'projectUri':lib.as_uri(),'libraries':[ml]}, {'projectUri':app.as_uri(),'libraries':[ml]}]
+    command(snapshot)
+    time.sleep(2)
+    state(single, 'single-after', True)
+    state(app, 'multi-after', True)
+    state(single, 'test-after', True, True)
+    assert all(raw(d) == before[str(d)] for d in [single,lib,app]), 'changed unowned entries'
+    # Simulate m2e removing the extra entries during a configuration update.
+    send({'method':'java/projectConfigurationsUpdate','params':{'identifiers':[{'uri':(d/'pom.xml').as_uri()} for d in [single,lib,app]]}})
+    time.sleep(3)
+    state(single, 'single-reimport', True)
+    state(app, 'multi-reimport', True)
+    assert all(raw(d) == before[str(d)] for d in [single,lib,app]), 'reimport changed unowned entries'
+    # A saved API change must replace the immutable binary directory.
+    (single/'src/main/java/probe/Channel.kt').write_text('package probe\nenum class Channel { SMS, EMAIL }\n')
+    state(single, 'single-during-rebuild', True)
+    changed = build(single, 'single-changed')[0]
+    snapshot[0]['libraries'] = [library(changed, 'single-changed'), library(changed, 'single-test-changed', True)]
+    command(snapshot)
+    time.sleep(2)
+    changed_state = state(single, 'single-new-enum-member', True)
+    assert any(label.startswith('EMAIL') for label in changed_state['completion'])
+    # Failed Kotlin compilation keeps both main and test APIs attached.
+    (single/'src/main/java/probe/Channel.kt').write_text('package probe\nenum class Channel { ??? }\n')
+    broken = build(single, 'single-broken', expected=False)[0]
+    assert any(g['status'] == 'failed' for g in broken['kotlinGoals'])
+    state(single, 'single-broken-retains-api', True)
+    state(single, 'single-broken-retains-test-api', True, True)
+    # A javac failure skips test Kotlin targets, so this whole snapshot is retained.
+    (single/'src/main/java/probe/Channel.kt').write_text('package probe\nenum class Delivery { SMS }\n')
+    skipped = build(single, 'single-skipped-test', expected=False)[0]
+    assert any(g['execution'].endswith(':test-compile') and g['status'] == 'skipped' for g in skipped['kotlinGoals'])
+    assert list(pathlib.Path(skipped['output']).rglob('Delivery.class'))
+    state(single, 'single-skipped-test-retains-api', True)
+    # The reactor fixture has no test Kotlin goal. Publish despite downstream javac failure.
+    kt = lib/'src/main/java/probe/Channel.kt'
+    kt.write_text('package probe\nenum class Delivery { SMS }\n')
+    renamed = build(multi, 'multi-renamed')
+    renamed_lib = next(m for m in renamed if 'channel-lib' in m['key'])
+    new_library = library(renamed_lib, 'multi-renamed', name='Delivery')
+    assert not list(pathlib.Path(renamed_lib['output']).rglob('Channel.class'))
+    snapshot[1]['libraries'] = snapshot[2]['libraries'] = [new_library]
+    command(snapshot)
+    state(app, 'multi-renamed', False)
+    kt.unlink()
+    snapshot[1]['libraries'] = snapshot[2]['libraries'] = []
+    command(snapshot)
+    state(app, 'multi-deleted', False)
+    kt.write_text('package probe\nenum class Channel { SMS }\n')
+    restored = next(m for m in build(multi, 'multi-restored') if 'channel-lib' in m['key'])
+    restored_library = library(restored, 'multi-restored')
+    snapshot[1]['libraries'] = snapshot[2]['libraries'] = [restored_library]
+    command(snapshot)
+    state(app, 'multi-restored', True)
+    (single/'src/main/java/probe/Channel.kt').write_text('package probe\nenum class Channel { SMS }\n')
+    repaired = build(single, 'single-repaired')[0]
+    snapshot[0]['libraries'] = [library(repaired, 'single-repaired'), library(repaired, 'single-test-repaired', True)]
+    command(snapshot)
+    time.sleep(2)
+    state(single, 'single-repaired', True)
+    # No old API after explicit invalidation, and recovery is repeatable.
+    command([])
+    time.sleep(2)
+    state(single, 'single-withdrawn', False)
+    state(app, 'multi-withdrawn', False)
+    state(single, 'test-withdrawn', False, True)
+    command(snapshot)
+    time.sleep(2)
+    state(single, 'single-recovered', True)
+    state(app, 'multi-recovered', True)
+    # Main sources must not gain visibility of test-only Kotlin libraries.
+    leak = single/'src/main/java/probe/MainLeak.java'
+    leak_source = test_source.replace('TestCaller', 'MainLeak')
+    leak.write_text(leak_source)
+    send({'method':'textDocument/didOpen','params':{'textDocument':{'uri':leak.as_uri(),'languageId':'java','version':1,'text':leak_source}}})
+    deadline = time.monotonic() + 30
+    while True:
+        time.sleep(0.25)
+        request('workspace/symbol', {'query':'MainLeak'})
+        reports = [m['params'] for m in transcript if m.get('method')=='textDocument/publishDiagnostics' and m['params']['uri']==leak.as_uri()]
+        if reports: break
+        assert time.monotonic() < deadline, 'no diagnostics for main/test isolation'
+    evidence['main-test-isolation'] = reports[-1]['diagnostics']
+    assert any(d.get('severity') == 1 for d in reports[-1]['diagnostics']), reports[-1]
+    # Compiler and JDT outputs must not share Kotlin classes.
+    assert not list(single.glob('target/classes/**/Channel.class'))
+    assert not list(lib.glob('target/classes/**/Channel.class'))
+    # -fae runs independent Kotlin modules and records upstream-skipped targets.
+    fail_reactor = work/'fail-at-end'
+    fail_reactor.mkdir()
+    (fail_reactor/'pom.xml').write_text(prefix + '<groupId>probe</groupId><artifactId>failure-reactor</artifactId><version>1</version><packaging>pom</packaging>' + properties + '<modules><module>broken-java</module><module>independent</module><module>downstream</module></modules></project>')
+    failure_parent = '<parent><groupId>probe</groupId><artifactId>failure-reactor</artifactId><version>1</version></parent>'
+    for name in ['broken-java', 'independent', 'downstream']:
+        module = fail_reactor/name
+        (module/'src/main/java/probe').mkdir(parents=True)
+        dependency = '<dependencies><dependency><groupId>probe</groupId><artifactId>broken-java</artifactId><version>1</version></dependency><dependency><groupId>org.jetbrains.kotlin</groupId><artifactId>kotlin-stdlib</artifactId><version>2.0.10</version></dependency></dependencies>' if name == 'downstream' else stdlib
+        (module/'pom.xml').write_text(prefix + failure_parent + '<artifactId>' + name + '</artifactId>' + dependency + plugin + '</project>')
+        if name == 'broken-java':
+            (module/'src/main/java/probe/Broken.java').write_text('package probe; public class Broken { Missing value; }')
+        else:
+            (module/'src/main/java/probe/Channel.kt').write_text('package probe\nenum class Channel { SMS }\n')
+    statuses = build(fail_reactor, 'fail-at-end-statuses', expected=False)
+    independent = next(m for m in statuses if ':independent:' in m['key'])
+    downstream = next(m for m in statuses if ':downstream:' in m['key'])
+    assert all(g['status'] == 'success' for g in independent['kotlinGoals']), independent
+    assert all(g['status'] == 'skipped' for g in downstream['kotlinGoals']), downstream
+    assert list(pathlib.Path(independent['output']).rglob('Channel.class'))
+    print(json.dumps(evidence, indent=2))
+finally:
+    (work/'evidence.json').write_text(json.dumps(evidence, indent=2))
+    (work/'transcript.json').write_text(json.dumps(transcript, indent=2))
+    proc.terminate()
+    proc.wait(timeout=20)
+    print('Evidence:', work, file=sys.stderr)
diff --git a/plugins/lombok/LICENSE b/plugins/lombok/LICENSE
new file mode 100644
index 000000000..465d9bf8f
--- /dev/null
+++ b/plugins/lombok/LICENSE
@@ -0,0 +1,104 @@
+Copyright (C) 2009-2021 The Project Lombok Authors.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+
+==============================================================================
+Licenses for included components:
+
+org.ow2.asm:asm
+org.ow2.asm:asm-analysis
+org.ow2.asm:asm-commons
+org.ow2.asm:asm-tree
+org.ow2.asm:asm-util
+ASM: a very small and fast Java bytecode manipulation framework
+ Copyright (c) 2000-2011 INRIA, France Telecom
+ All rights reserved.
+
+ Redistribution and use in source and binary forms, with or without
+ modification, are permitted provided that the following conditions
+ are met:
+ 1. Redistributions of source code must retain the above copyright
+    notice, this list of conditions and the following disclaimer.
+ 2. Redistributions in binary form must reproduce the above copyright
+    notice, this list of conditions and the following disclaimer in the
+    documentation and/or other materials provided with the distribution.
+ 3. Neither the name of the copyright holders nor the names of its
+    contributors may be used to endorse or promote products derived from
+    this software without specific prior written permission.
+
+ THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
+ THE POSSIBILITY OF SUCH DAMAGE.
+
+------------------------------------------------------------------------------
+rzwitserloot/com.zwitserloot.cmdreader
+
+ Copyright © 2010 Reinier Zwitserloot.
+
+ Permission is hereby granted, free of charge, to any person obtaining a copy
+ of this software and associated documentation files (the "Software"), to deal
+ in the Software without restriction, including without limitation the rights
+ to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ copies of the Software, and to permit persons to whom the Software is
+ furnished to do so, subject to the following conditions:
+
+ The above copyright notice and this permission notice shall be included in
+ all copies or substantial portions of the Software.
+
+ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ THE SOFTWARE.
+
+------------------------------------------------------------------------------
+
+projectlombok/lombok.patcher
+
+ Copyright (C) 2009-2021 The Project Lombok Authors.
+
+ Permission is hereby granted, free of charge, to any person obtaining a copy
+ of this software and associated documentation files (the "Software"), to deal
+ in the Software without restriction, including without limitation the rights
+ to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ copies of the Software, and to permit persons to whom the Software is
+ furnished to do so, subject to the following conditions:
+
+ The above copyright notice and this permission notice shall be included in
+ all copies or substantial portions of the Software.
+
+ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ THE SOFTWARE.
+
+------------------------------------------------------------------------------
diff --git a/plugins/lombok/README.md b/plugins/lombok/README.md
new file mode 100644
index 000000000..701198345
--- /dev/null
+++ b/plugins/lombok/README.md
@@ -0,0 +1,71 @@
+# Lombok agent for JDT LS
+
+`lombok-1.18.48-openidea.1.jar` is the app-provided Java agent for JDT LS. It includes
+[projectlombok/lombok#4059](https://github.com/projectlombok/lombok/pull/4059), which restores
+`lombok.config` lookup after Equinox removed `getModuleClassLoader(boolean)`.
+
+The jar is embedded by `ide-tools`, so every platform receives the same bytes without a download.
+Both Java server startup and launch diagnostics obtain it through `managed_bundle`. Tool detection
+reports the same version and path, replacing older IDE-installed official agents automatically.
+An explicit user `-javaagent` still takes precedence. Project Maven/Gradle dependencies are unchanged.
+The filename includes the patch version because JDT LS workspace keys include the agent path;
+changing agents must rebuild classes produced by the old agent. Old jars remain for running windows.
+
+Replace this temporary bundle with an official Maven Central release once that release includes
+#4059. Restore the registry's Maven Central install method and remove the embedded jar. Keep the
+workspace migration test when changing its path.
+
+## Provenance and build
+
+- Repository: https://github.com/projectlombok/lombok
+- Base tag: `v1.18.48` (`b48657c83ce44d027984f539bd36048293ce5e8e`).
+- Cherry-picked commits from PR #4059, in order:
+  - `2d535482a913de46c27d06c5b0b294918ede3f9c`
+  - `3098f4dd78b5349c2f382e7310e64db810dd380b`
+- Upstream version: `1.18.48`; `openidea.1` identifies this distribution of the patched agent.
+  Upstream's own `java -jar ... --version` still reports `1.18.48`.
+- SHA-256: `10f5cd1a32b946d3ff1c075735b94f35fffdbac11dea2be29d24dbf591dd51a4`
+- License: [MIT, including bundled component notices](LICENSE), also retained inside the jar.
+- Build environment: macOS arm64, OpenJDK 23.0.1, Apache Ant 1.10.15, upstream Ivy setup.
+
+Build using the upstream Ant entry point described in its contributing guide:
+
+```sh
+git clone https://github.com/projectlombok/lombok.git
+cd lombok
+git checkout -b openidea-1.18.48 v1.18.48
+git fetch https://github.com/chagong/lombok.git fix-equinox-bundle-wiring
+git cherry-pick 2d535482a913de46c27d06c5b0b294918ede3f9c 3098f4dd78b5349c2f382e7310e64db810dd380b
+ant dist
+cp dist/lombok.jar /path/to/openidea/plugins/lombok/lombok-1.18.48-openidea.1.jar
+```
+
+The changelog context conflicts because the first commit adds a release-note line under the
+older development heading and the second removes it. Resolve mechanically by adding then removing
+only that line, retaining the complete v1.18.48 changelog. The final source diff from v1.18.48 changes
+only `src/eclipseAgent/lombok/launch/PatchFixesHider.java`, `test/core/src/lombok/TestEclipse.java`,
+and `test/core/src/lombok/launch/PatchFixesHiderTest.java`; no other Java source changes were made.
+In the build checkout, the two remote resolvers in
+`buildScripts/ivysettings.xml` were reordered to try Maven Central before Eclipse staging; the
+local resolver and all dependency coordinates were retained. The JVM was configured to use the
+local HTTP/HTTPS proxy for downloads. Ant's timestamps mean a rebuild need not be byte-identical;
+`SHA256SUMS` records the checked-in artifact and is verified by the Rust regression tests.
+
+## Validation
+
+A parent POM with DTO and application modules uses Lombok 1.18.46. Root `lombok.config` enables
+`config.stopBubbling = true` and `lombok.accessors.chain = true`.
+
+On macOS arm64 with JDT LS 1.63.0 / Equinox 3.25.0, server OpenJDK 25 and project JDK 21:
+
+- Official 1.18.46 and 1.18.48 agents generated `void` setters; the following Maven incremental
+  build reused the DTO classes and failed with `void cannot be dereferenced`.
+- This agent passed five fresh project/workspace builds. `javap` confirmed setters returning
+  the DTO class; the following Maven incremental install passed.
+- Without `lombok.config`, both official 1.18.48 and patched agents built successfully and produced
+  identical `javap` output, including default `void` setters.
+- Upstream `PatchFixesHiderTest` passed both the standard OSGi and legacy Equinox lookup tests.
+
+Windows and Linux runtime validation has not been performed. Rust tests cover source selection
+for both supported architectures on all three OS variants, offline provisioning, corruption
+repair, concurrent windows, explicit user overrides, and JDT LS workspace migration.
diff --git a/plugins/lombok/SHA256SUMS b/plugins/lombok/SHA256SUMS
new file mode 100644
index 000000000..67cbcd675
--- /dev/null
+++ b/plugins/lombok/SHA256SUMS
@@ -0,0 +1 @@
+10f5cd1a32b946d3ff1c075735b94f35fffdbac11dea2be29d24dbf591dd51a4  lombok-1.18.48-openidea.1.jar
diff --git a/plugins/lombok/lombok-1.18.48-openidea.1.jar b/plugins/lombok/lombok-1.18.48-openidea.1.jar
new file mode 100644
index 000000000..d8a4dce2f
Binary files /dev/null and b/plugins/lombok/lombok-1.18.48-openidea.1.jar differ
diff --git a/src-tauri/Cargo.toml b/src-tauri/Cargo.toml
index 909f3e638..5ebf05c5e 100644
--- a/src-tauri/Cargo.toml
+++ b/src-tauri/Cargo.toml
@@ -76,3 +76,5 @@ objc2 = "0.6"
 objc2-app-kit = { version = "0.3", default-features = false, features = ["std", "NSApplication", "NSButton", "NSResponder", "NSView", "NSWindow"] }
 objc2-core-foundation = { version = "0.3", default-features = false, features = ["std", "block2", "CFRunLoop"] }
 objc2-foundation = { version = "0.3", default-features = false, features = ["std", "block2", "NSNotification", "NSOperation", "NSString"] }
+# Used only by the debug font-restriction override; Cargo dependency cfg cannot test debug_assertions.
+objc2-web-kit = { version = "0.3", default-features = false, features = ["std", "WKWebViewConfiguration", "WKPreferences"] }
diff --git a/src-tauri/src/commands/fonts.rs b/src-tauri/src/commands/fonts.rs
index 705da8e2d..8a27a0faa 100644
--- a/src-tauri/src/commands/fonts.rs
+++ b/src-tauri/src/commands/fonts.rs
@@ -13,3 +13,13 @@ pub async fn system_font_families(refresh: bool) -> IdeResult<Vec<FontFamily>> {
         .await
         .map_err(|e| IdeError::internal(e.to_string()))
 }
+
+/// Raw font bundle, selected by family, never by a frontend-supplied path.
+#[tauri::command]
+pub async fn user_font_data(family: String) -> IdeResult<tauri::ipc::Response> {
+    tauri::async_runtime::spawn_blocking(move || ide_fonts::user_font_data(&family))
+        .await
+        .map_err(|e| IdeError::internal(e.to_string()))?
+        .map(tauri::ipc::Response::new)
+        .map_err(|e| IdeError::invalid(e.to_string()))
+}
diff --git a/src-tauri/src/commands/fs.rs b/src-tauri/src/commands/fs.rs
index 5ff8d0f10..efa29a9b5 100644
--- a/src-tauri/src/commands/fs.rs
+++ b/src-tauri/src/commands/fs.rs
@@ -5,6 +5,38 @@ use ide_vfs::FileEntry;
 use std::path::PathBuf;
 use tauri::{State, Window};
 
+#[tauri::command]
+#[specta::specta]
+pub async fn fs_entry_kind(state: State<'_, AppState>, path: PathBuf) -> IdeResult<ide_vfs::EntryKind> {
+    fs::entry_kind(&state.host, path).await
+}
+
+#[tauri::command]
+#[specta::specta]
+pub async fn fs_compare_directories(
+    window: Window,
+    state: State<'_, AppState>,
+    left: PathBuf,
+    right: PathBuf,
+    request: ide_core::RequestId,
+    on_progress: tauri::ipc::Channel<ide_vfs::DirectoryCompareProgress>,
+) -> IdeResult<Vec<ide_vfs::DirectoryCompareEntry>> {
+    fs::compare_directories(&state.host, window.label(), left, right, request, super::sender(on_progress)).await
+}
+
+#[tauri::command]
+#[specta::specta]
+pub async fn fs_copy_merge(
+    window: Window,
+    state: State<'_, AppState>,
+    source_root: PathBuf,
+    destination_root: PathBuf,
+    path: PathBuf,
+    overwrite: bool,
+) -> IdeResult<()> {
+    fs::copy_merge(&state.host, window.label(), source_root, destination_root, path, overwrite).await
+}
+
 #[tauri::command]
 #[specta::specta]
 pub fn fs_read_dir(window: Window, state: State<'_, AppState>, path: PathBuf) -> IdeResult<Vec<FileEntry>> {
diff --git a/src-tauri/src/commands/lsp.rs b/src-tauri/src/commands/lsp.rs
index c311cb8eb..765d7e755 100644
--- a/src-tauri/src/commands/lsp.rs
+++ b/src-tauri/src/commands/lsp.rs
@@ -95,8 +95,8 @@ pub async fn lsp_implementations(
     ide_host::ops::lsp::lsp_implementations(&state.host, window.label(), request, doc, positions).await
 }
 
-/// Contents of a virtual document (library class, decompiled code) that a
-/// language server returned a non-`file:` URI for. Cached per project.
+/// Contents of a read-only language-server document, including JDT library
+/// classes and disk class files. Cached per project.
 #[tauri::command]
 #[specta::specta]
 pub async fn lsp_virtual_document(
@@ -107,6 +107,16 @@ pub async fn lsp_virtual_document(
     ide_host::ops::lsp::lsp_virtual_document(&state.host, window.label(), uri).await
 }
 
+#[tauri::command]
+#[specta::specta]
+pub async fn lsp_resolve_class_file(
+    window: Window,
+    state: State<'_, AppState>,
+    path: std::path::PathBuf,
+) -> IdeResult<String> {
+    ide_host::ops::lsp::lsp_resolve_class_file(&state.host, window.label(), path).await
+}
+
 /// References of the symbol at `pos`. `project_wide` also searches project files
 /// outside the language server's analysis scope; bulk scans over many symbols
 /// leave it off. Cancel with `cancel_request(request)`.
diff --git a/src-tauri/src/commands/mod.rs b/src-tauri/src/commands/mod.rs
index 5111d421b..c71ce8405 100644
--- a/src-tauri/src/commands/mod.rs
+++ b/src-tauri/src/commands/mod.rs
@@ -126,6 +126,7 @@ pub fn builder() -> tauri_specta::Builder<tauri::Wry> {
         notebook::notebook_interrupt,
         notebook::notebook_restart,
         fs::fs_read_dir,
+        fs::fs_entry_kind,
         bytes::fs_probe,
         bytes::fs_read_range,
         bytes::fs_read_image,
@@ -136,6 +137,8 @@ pub fn builder() -> tauri_specta::Builder<tauri::Wry> {
         fs::fs_set_writable,
         fs::fs_delete,
         fs::fs_copy,
+        fs::fs_copy_merge,
+        fs::fs_compare_directories,
         fs::fs_read_text,
         clipboard::clipboard_file_list,
         clipboard::clipboard_has_files,
@@ -201,6 +204,7 @@ pub fn builder() -> tauri_specta::Builder<tauri::Wry> {
         lsp::lsp_goto,
         lsp::lsp_implementations,
         lsp::lsp_virtual_document,
+        lsp::lsp_resolve_class_file,
         lsp::lsp_references,
         lsp::lsp_document_highlights,
         lsp::lsp_workspace_symbols,
diff --git a/src-tauri/src/lib.rs b/src-tauri/src/lib.rs
index 2af828bb3..4cfeb1ff0 100644
--- a/src-tauri/src/lib.rs
+++ b/src-tauri/src/lib.rs
@@ -87,7 +87,12 @@ pub fn run() {
     // Paths macOS asked to open (Finder's Open With, the Dock) before setup ran: the first window takes them.
     let early_opens: Arc<Mutex<Option<Vec<PathBuf>>>> = Arc::default();
     let setup_opens = early_opens.clone();
-    let invoke = Arc::new(builder.invoke_handler());
+    let typed_invoke = builder.invoke_handler();
+    // Raw Response is not a JSON/Specta type; keep the binary command out of generated bindings.
+    let raw_invoke: fn(tauri::ipc::Invoke) -> bool = tauri::generate_handler![commands::fonts::user_font_data];
+    let invoke = Arc::new(move |request: tauri::ipc::Invoke| {
+        if request.message.command() == "user_font_data" { raw_invoke(request) } else { typed_invoke(request) }
+    });
     app.invoke_handler(move |request| {
         let webview = request.message.webview_ref();
         if let Some(state) = webview.try_state::<AppState>() {
diff --git a/src-tauri/src/windows.rs b/src-tauri/src/windows.rs
index 0108a4b97..54b6a35ce 100644
--- a/src-tauri/src/windows.rs
+++ b/src-tauri/src/windows.rs
@@ -299,7 +299,7 @@ fn build_project_window(app: &AppHandle, mut config: WindowConfig) -> IdeResult<
         config.background_color = Some(frame_color(a, false));
     }
     let window = WebviewWindowBuilder::from_config(app, &config)
-        .and_then(|b| b.build())
+        .and_then(|b| dev_font_preferences(b).build())
         .map_err(|e| IdeError::internal(format!("cannot create window: {e}")))?;
     apply_zoom(app, &window);
     #[cfg(target_os = "macos")]
@@ -771,7 +771,7 @@ pub fn open_settings_window(
     #[cfg(not(target_os = "macos"))]
     let builder = builder.and_then(|b| b.parent(&parent));
     let window = builder
-        .and_then(|b| b.build())
+        .and_then(|b| dev_font_preferences(b).build())
         .map_err(|e| IdeError::internal(format!("cannot create settings window: {e}")))?;
     apply_zoom(app, &window);
     #[cfg(target_os = "macos")]
@@ -885,6 +885,39 @@ fn centered(px: f64, py: f64, pw: f64, ph: f64, w: f64, h: f64) -> (f64, f64) {
     (px + (pw - w) / 2.0, py + ((ph - h) / 2.0).max(0.0))
 }
 
+/// Reproduce WKWebView's user-font restriction before WKWebView creation. The
+/// private selector and environment override are absent from release builds.
+#[cfg(all(debug_assertions, target_os = "macos"))]
+fn dev_font_preferences(
+    builder: WebviewWindowBuilder<'_, tauri::Wry, AppHandle>,
+) -> WebviewWindowBuilder<'_, tauri::Wry, AppHandle> {
+    if std::env::var("OPENIDEA_DEV_DISALLOW_USER_FONTS").as_deref() == Ok("1") {
+        use objc2::{MainThreadMarker, msg_send, sel};
+        use objc2_foundation::NSObjectProtocol;
+        let config = unsafe {
+            objc2_web_kit::WKWebViewConfiguration::new(MainThreadMarker::new().expect("window creation on main thread"))
+        };
+        let preferences = unsafe { config.preferences() };
+        if preferences.respondsToSelector(sel!(_setShouldAllowUserInstalledFonts:)) {
+            unsafe {
+                let _: () = msg_send![&preferences, _setShouldAllowUserInstalledFonts: false];
+            }
+            let allowed: bool = unsafe { msg_send![&preferences, _shouldAllowUserInstalledFonts] };
+            tracing::info!(allowed, "Development user-installed fonts override");
+            return builder.with_webview_configuration(config);
+        }
+        tracing::warn!("WKPreferences user-font development selector unavailable");
+    }
+    builder
+}
+
+#[cfg(not(all(debug_assertions, target_os = "macos")))]
+fn dev_font_preferences(
+    builder: WebviewWindowBuilder<'_, tauri::Wry, AppHandle>,
+) -> WebviewWindowBuilder<'_, tauri::Wry, AppHandle> {
+    builder
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/src/bindings.ts b/src/bindings.ts
index a70080cf7..c3d5811cd 100644
--- a/src/bindings.ts
+++ b/src/bindings.ts
@@ -145,6 +145,7 @@ export const commands = {
 	notebookInterrupt: (id: string) => typedError<null, IdeError>(__TAURI_INVOKE("notebook_interrupt", { id })),
 	notebookRestart: (id: string) => typedError<NotebookSnapshot, IdeError>(__TAURI_INVOKE("notebook_restart", { id })),
 	fsReadDir: (path: string) => typedError<FileEntry[], IdeError>(__TAURI_INVOKE("fs_read_dir", { path })),
+	fsEntryKind: (path: string) => typedError<EntryKind, IdeError>(__TAURI_INVOKE("fs_entry_kind", { path })),
 	/**  Size and text/binary classification, from the file's head only. */
 	fsProbe: (path: string) => typedError<FileProbe, IdeError>(__TAURI_INVOKE("fs_probe", { path })),
 	/**  Up to `len` bytes from `offset` (capped per call), base64-encoded. */
@@ -167,6 +168,8 @@ export const commands = {
 	/**  Moving to the trash can take a while (large trees): kept off the main thread. */
 	fsDelete: (path: string) => typedError<null, IdeError>(__TAURI_INVOKE("fs_delete", { path })),
 	fsCopy: (from: string, to: string) => typedError<null, IdeError>(__TAURI_INVOKE("fs_copy", { from, to })),
+	fsCopyMerge: (sourceRoot: string, destinationRoot: string, path: string, overwrite: boolean) => typedError<null, IdeError>(__TAURI_INVOKE("fs_copy_merge", { sourceRoot, destinationRoot, path, overwrite })),
+	fsCompareDirectories: (left: string, right: string, request: RequestId, onProgress: Channel<DirectoryCompareProgress>) => typedError<DirectoryCompareEntry[], IdeError>(__TAURI_INVOKE("fs_compare_directories", { left, right, request, onProgress })),
 	/**
 	 *  Reads a text file without opening it as a document (previews, quick
 	 *  definition). Prefers the unsaved buffer when the file is open.
@@ -372,10 +375,11 @@ export const commands = {
 	 */
 	lspImplementations: (request: RequestId, doc: DocId, positions: Pos[]) => typedError<Location[][], IdeError>(__TAURI_INVOKE("lsp_implementations", { request, doc, positions })),
 	/**
-	 *  Contents of a virtual document (library class, decompiled code) that a
-	 *  language server returned a non-`file:` URI for. Cached per project.
+	 *  Contents of a read-only language-server document, including JDT library
+	 *  classes and disk class files. Cached per project.
 	 */
 	lspVirtualDocument: (uri: string) => typedError<VirtualDocument, IdeError>(__TAURI_INVOKE("lsp_virtual_document", { uri })),
+	lspResolveClassFile: (path: string) => typedError<string, IdeError>(__TAURI_INVOKE("lsp_resolve_class_file", { path })),
 	/**
 	 *  References of the symbol at `pos`. `project_wide` also searches project files
 	 *  outside the language server's analysis scope; bulk scans over many symbols
@@ -1418,6 +1422,8 @@ export type AppearanceSettings = {
 	/**  Apply `ui_font_family` / `ui_font_size` (otherwise the theme's). */
 	useCustomFont?: boolean,
 	uiFontFamily?: string,
+	/**  Font tried when `ui_font_family` lacks a glyph; empty = none. */
+	uiFontFallback?: string,
 	contrastScrollbars?: boolean,
 	/**  Adjust colours for red-green vision deficiency. */
 	redGreenVision?: boolean,
@@ -1434,6 +1440,7 @@ export type AppearanceSettings = {
 	editorAntialiasing?: string,
 	showToolWindowBars?: boolean,
 	showToolWindowNames?: boolean,
+	showToolWindowBadges?: boolean,
 	widescreenToolWindows?: boolean,
 	/**
 	 *  Status bar widgets shown (`true`) or hidden (`false`) by the user
@@ -2511,6 +2518,25 @@ export type Diagnostic = {
 	server?: string | null,
 };
 
+export type DirectoryCompareEntry = {
+	path: string,
+	status: DirectoryCompareStatus,
+	leftKind: EntryKind | null,
+	rightKind: EntryKind | null,
+	leftLink?: string | null,
+	rightLink?: string | null,
+};
+
+export type DirectoryCompareProgress = {
+	scanned: number,
+	compared: number,
+	total: number | null,
+	bytesRead: number | null,
+	path: string,
+};
+
+export type DirectoryCompareStatus = "leftOnly" | "rightOnly" | "different" | "equal";
+
 /**  Changes under a folder (Show History on a directory). */
 export type DirectoryHistory = {
 	/**  Snapshots of files under the folder and labels, newest first. */
@@ -2949,9 +2975,11 @@ export type EnvReloaded = {
 	shellRead: boolean,
 };
 
+export type ErrorData = { type: "tool"; tool: string; missing: boolean };
+
 export type ErrorKind = "notFound" | "alreadyExists" | "permissionDenied" | "invalidInput" | 
 /**  Document version mismatch; the UI must resync the full text. */
-"outOfSync" | "cancelled" | 
+"outOfSync" | "cancelled" | "timedOut" | 
 /**  A required external tool (language server, git, debugger) is unavailable. */
 "unavailable" | "io" | "protocol" | "internal";
 
@@ -3181,6 +3209,7 @@ export type FormField = {
 export type FormatOptions = {
 	tabSize: number,
 	insertSpaces: boolean,
+	onSave?: boolean,
 };
 
 /**  One occurrence of a duplicated code fragment. */
@@ -3517,6 +3546,8 @@ export type HunkRange = {
 export type IdeError = {
 	kind: ErrorKind,
 	message: string,
+	/**  Structured detail for errors the UI acts on; `null` for plain errors. */
+	data?: ErrorData | null,
 };
 
 export type IdeEvent = 
@@ -4002,6 +4033,7 @@ export type LanguagesSettings = {
 	rust?: RustSettings,
 	go?: GoSettings,
 	typescript?: TypeScriptSettings,
+	prettier?: PrettierSettings,
 	java?: JavaSettings,
 };
 
@@ -4745,6 +4777,15 @@ export type PreparedRequest = {
 	body: string | null,
 };
 
+export type PrettierSettings = {
+	/**  Empty path: project node_modules, managed installation, then PATH. */
+	path?: string,
+	languages?: string[],
+	/**  Prefer Prettier even when a language server offers formatting. */
+	prefer?: boolean,
+	runOnSave?: boolean,
+};
+
 /**  Memory of one row of the breakdown. */
 export type ProcessMemory = {
 	category: MemoryCategory,
@@ -6160,7 +6201,7 @@ export type ToolInfo = {
 
 export type ToolKind = "languageServer" | "debugger" | 
 /**  Loaded into another tool's process, e.g. a jdtls agent. */
-"plugin";
+"plugin" | "formatter";
 
 export type ToolSettings = {
 	/**  Executable to launch instead of the managed / `PATH` one; empty = auto-detect. */
@@ -6309,7 +6350,7 @@ export type VirtualDocument = {
 	title: string,
 	/**  Origin shown in the tooltip / banner, e.g. the jar path. */
 	description: string | null,
-	/**  Generated by a decompiler / disassembler rather than real sources. */
+	/**  Generated Java from a decompiler, rather than real source or a disassembler stub. */
 	decompiled: boolean,
 };
 
diff --git a/src/editor/api.ts b/src/editor/api.ts
index 8ce6db51b..9f2ab9a0f 100644
--- a/src/editor/api.ts
+++ b/src/editor/api.ts
@@ -42,7 +42,7 @@ export interface EditorDocContext {
   /**
    * A read-only virtual document (library class contents from a language
    * server); `path` is then its URI, not a file: skip file-based features
-   * (VCS, local history, TODO scanning, breakpoints…).
+   * (VCS, local history, TODO scanning…). JDT class documents support breakpoints.
    */
   virtual?: boolean;
 }
diff --git a/src/editor/core/backend.ts b/src/editor/core/backend.ts
index 5c2250168..8e4b020cf 100644
--- a/src/editor/core/backend.ts
+++ b/src/editor/core/backend.ts
@@ -36,7 +36,7 @@ export interface DocPatchedEvent {
 
 export interface DocBackend {
   open(path: string): Promise<DocumentInfo>;
-  /** Opens the read-only virtual document behind a non-`file:` URI (library class contents). */
+  /** Opens a read-only language-server document (library or disk class contents). */
   openVirtual(uri: string): Promise<DocumentInfo>;
   close(doc: DocId): Promise<void>;
   edit(doc: DocId, baseVersion: number, changes: TextChange[]): Promise<number>;
diff --git a/src/editor/core/controller.ts b/src/editor/core/controller.ts
index be343fbf4..90e12af6d 100644
--- a/src/editor/core/controller.ts
+++ b/src/editor/core/controller.ts
@@ -89,6 +89,7 @@ import { NavigationHistory } from "./model/navHistory";
 import { EditHistory } from "./model/editHistory";
 import { loadSession, restoreTabsState, serializeSession, storeSession, type FileViewState } from "./model/session";
 import { docBackend, type DocBackend } from "./backend";
+import { isClassFile } from "@/platform/classFiles";
 import { isVirtualUri, virtualDocument } from "@/platform/virtualDocs";
 import type { VirtualDocument } from "@/platform/ipc";
 import type { Scheduler } from "./sync/DocSync";
@@ -860,9 +861,21 @@ export class EditorController implements SlotHost {
       throw new Error("The project is closing");
   }
 
-  async openFile(path: string, o: OpenOptions = {}) {
+  async openFile(path: string, o: OpenOptions = {}): Promise<void> {
     const generation = this.openingGeneration();
     if (isVirtualUri(path)) return this.openVirtual(path, o);
+    if (isClassFile(path)) {
+      await this.projectTransition;
+      this.checkOpening(generation);
+      try {
+        const target = await call(commands.lspResolveClassFile(path));
+        this.checkOpening(generation);
+        return isVirtualUri(target) ? this.openVirtual(target, o) : this.openFile(target, o);
+      } catch (e) {
+        notifications().notify({ level: "warning", title: "Cannot open library class", body: String(e), group: "lsp" });
+        return;
+      }
+    }
     await this.projectTransition;
     this.checkOpening(generation);
     // Images, binary and huge files open in a contributed viewer unless already open as text.
@@ -901,6 +914,7 @@ export class EditorController implements SlotHost {
   }
 
   async openInput(input: EditorInput, o: OpenOptions = {}) {
+    if (input.path && isClassFile(input.path)) return this.openFile(input.path, o);
     return this.admitInput(input, o, this.openingGeneration());
   }
 
diff --git a/src/editor/core/view/Banner.tsx b/src/editor/core/view/Banner.tsx
index 0023ee02a..963665f22 100644
--- a/src/editor/core/view/Banner.tsx
+++ b/src/editor/core/view/Banner.tsx
@@ -3,6 +3,7 @@ import { Icon, T } from "@/ui";
 import { useEditorBanners, type EditorBannerContribution } from "@/workbench/contributions";
 import { useDocMeta } from "../model/document";
 import styles from "./EditorArea.module.css";
+import { classFileBreakpointReason } from "@/platform/classFiles";
 import { tx } from "@/platform/i18n";
 
 const TEXT = {
@@ -28,12 +29,22 @@ export const documentBanner: EditorBannerContribution = {
  * Notice above a library class opened from a language server (IDEA's
  * "Decompiled .class file" / library source bar): read-only, with its origin.
  */
-export function VirtualBanner({ decompiled, description }: { decompiled: boolean; description: string | null }) {
+export function VirtualBanner({
+  decompiled,
+  description,
+  path,
+}: {
+  decompiled: boolean;
+  description: string | null;
+  path: string;
+}) {
+  const reason = classFileBreakpointReason(path);
   return (
     <div className={`${styles.banner} ${styles.libraryBanner}`} role="status">
       <Icon name={decompiled ? "info" : "lock"} size={14} className={styles.bannerIcon} />
-      <span className={styles.bannerText}>
+      <span className={styles.virtualBannerText}>
         {decompiled ? tx("Decompiled .class file: sources are not available.") : tx("Library source (read-only).")}
+        {reason && ` ${tx(reason)}`}
       </span>
       {description && (
         <span className={styles.bannerDetail} title={description}>
diff --git a/src/editor/core/view/EditorArea.module.css b/src/editor/core/view/EditorArea.module.css
index 40fbc0dd1..593cd1ac4 100644
--- a/src/editor/core/view/EditorArea.module.css
+++ b/src/editor/core/view/EditorArea.module.css
@@ -90,6 +90,10 @@
   background: var(--bg-feedback-warning);
   border-bottom-color: var(--border-feedback-warning);
 }
+.virtualBannerText {
+  min-width: 0;
+  padding: 8px 0;
+}
 .bannerText {
   flex: none;
   white-space: nowrap;
diff --git a/src/editor/core/view/EditorArea.tsx b/src/editor/core/view/EditorArea.tsx
index bd4b709a3..cc172aa56 100644
--- a/src/editor/core/view/EditorArea.tsx
+++ b/src/editor/core/view/EditorArea.tsx
@@ -398,7 +398,7 @@ function PaneContent({ paneId, tab, tabsVisible }: { paneId: string; tab: Tab; t
     return (
       <>
         {virtual ? (
-          <VirtualBanner decompiled={virtual.decompiled} description={virtual.description} />
+          <VirtualBanner path={tab.input.path!} decompiled={virtual.decompiled} description={virtual.description} />
         ) : (
           <EditorBanners path={tab.input.path} />
         )}
diff --git a/src/editor/core/virtual.test.ts b/src/editor/core/virtual.test.ts
index e4417eb4d..aaa464afa 100644
--- a/src/editor/core/virtual.test.ts
+++ b/src/editor/core/virtual.test.ts
@@ -10,7 +10,7 @@ vi.mock("@/platform/virtualDocs", async (importOriginal) => {
   return {
     ...actual,
     virtualDocument: vi.fn(async (uri: string): Promise<VirtualDocument> => {
-      if (uri !== JDT) throw new Error(`no contents for ${uri}`);
+      if (uri !== JDT && uri !== "file:///p/target/classes/Lib.class") throw new Error(`no contents for ${uri}`);
       return {
         uri,
         text: TEXT,
@@ -30,6 +30,7 @@ const { serializeSession } = await import("./model/session");
 const { useDocMeta } = await import("./model/document");
 const { registerMenuGroup } = await import("@/workbench/contributions");
 const { registerActions } = await import("@/platform/actions");
+const { commands } = await import("@/platform/ipc");
 const { resolveMenuItems } = await import("@/ui");
 
 let ctrl: InstanceType<typeof EditorController> | null = null;
@@ -55,6 +56,24 @@ describe("virtual editor input", () => {
     expect(isTextInput({ kind: "diff", key: "d" })).toBe(false);
   });
 
+  it.each([
+    ["/m2/lib.jar!/org/example/Lib.class", JDT, "virtual"],
+    ["/p/target/classes/Lib.class", "/p/Lib.java", "file"],
+    ["/p/build/classes/Lib.class", "file:///p/target/classes/Lib.class", "virtual"],
+  ])("routes %s before choosing a binary viewer", async (path, target, kind) => {
+    const resolve = vi.spyOn(commands, "lspResolveClassFile").mockResolvedValue({ status: "ok", data: target });
+    ctrl = new EditorController(createMemoryBackend({ [target]: TEXT }));
+    ctrl.start();
+    try {
+      await ctrl.openFile(path!, { focus: false });
+      expect(resolve).toHaveBeenCalledWith(path);
+      expect(activeTab().input).toMatchObject({ path: target, kind });
+      expect(ctrl.slotFor(activeTab().id)!.model.ctx().readOnly).toBe(kind === "virtual");
+    } finally {
+      resolve.mockRestore();
+    }
+  });
+
   it("opens a URI read-only at the target and keeps it out of the saved session", async () => {
     ctrl = new EditorController(createMemoryBackend({ "/p/App.java": "class App {}\n", [JDT]: TEXT }));
     ctrl.start();
diff --git a/src/editor/lsp/actions.ts b/src/editor/lsp/actions.ts
index 44ca77656..f774f6779 100644
--- a/src/editor/lsp/actions.ts
+++ b/src/editor/lsp/actions.ts
@@ -5,6 +5,7 @@ import { executeAction, registerActions, type Action } from "@/platform/actions"
 import { activeEditor, editorsFor, registerSaveParticipant, type TextEditorHandle } from "@/editor/api";
 import { maybeEditorService } from "@/workbench/contributions";
 import { useProject } from "@/platform/project";
+import { validateLanguages } from "@/platform/languageSettings";
 import { explicitCompletion } from "./completion";
 import { triggerSignatureHelp } from "./signature";
 import { quickDefinition, quickDocumentation } from "./hover";
@@ -122,8 +123,15 @@ export function registerFormatOnSave(): () => void {
     id: "lsp.formatOnSave",
     order: 50,
     beforeSave: async (ctx, handle) => {
-      if (!handle || ctx.readOnly || !useProject.getState().settings?.editor?.formatOnSave) return;
-      await formatDocument(handle.view, { explicit: false, selectionOnly: false });
+      const settings = useProject.getState().settings;
+      const prettier = validateLanguages(settings?.languages).prettier;
+      if (
+        !handle ||
+        ctx.readOnly ||
+        (!settings?.editor?.formatOnSave && !(prettier.runOnSave && prettier.languages.includes(ctx.language)))
+      )
+        return;
+      await formatDocument(handle.view, { explicit: false, selectionOnly: false, onSave: true });
     },
   });
 }
diff --git a/src/editor/lsp/format.module.css b/src/editor/lsp/format.module.css
new file mode 100644
index 000000000..54460af1f
--- /dev/null
+++ b/src/editor/lsp/format.module.css
@@ -0,0 +1,3 @@
+.diagnostics {
+  white-space: pre-wrap;
+}
diff --git a/src/editor/lsp/format.test.ts b/src/editor/lsp/format.test.ts
index 75c31b429..8f21dd7c7 100644
--- a/src/editor/lsp/format.test.ts
+++ b/src/editor/lsp/format.test.ts
@@ -1,5 +1,9 @@
-import { describe, expect, it } from "vitest";
-import { Text } from "@codemirror/state";
+import { describe, expect, it, vi } from "vitest";
+import { EditorState, Text } from "@codemirror/state";
+import { EditorView } from "@codemirror/view";
+import { CONTRIBUTED_FORMAT } from "@/editor/api";
+import { useProject } from "@/platform/project";
+import type { Settings } from "@/bindings";
 import {
   formatExcluded,
   guardFormatChanges,
@@ -7,7 +11,7 @@ import {
   protectedRegions,
   type FormatGuardOptions,
 } from "@/platform/formatGuard";
-import { dedentsToColumnZero, formattedLines } from "./format";
+import { dedentsToColumnZero, formatDocument, formattedLines } from "./format";
 
 describe("formattedLines", () => {
   const doc = Text.of(["fn  main(){", "let x=1;", "}", "", "fn other() {}"]);
@@ -105,3 +109,28 @@ describe("dedentsToColumnZero", () => {
     expect(dedentsToColumnZero("fun f() {}\n", "fun f() { }\n")).toBe(false);
   });
 });
+
+describe("format on save provider isolation", () => {
+  it("does not enable contributed formatters when only Prettier save is enabled", async () => {
+    const previous = useProject.getState();
+    const formatter = vi.fn(() => [{ from: 0, to: 6, insert: "SELECT" }]);
+    const view = new EditorView({
+      state: EditorState.create({
+        doc: "select",
+        extensions: [EditorState.languageData.of(() => [{ [CONTRIBUTED_FORMAT]: formatter }])],
+      }),
+    });
+    try {
+      const settings = { editor: { formatOnSave: false }, languages: { prettier: { runOnSave: true } } } as Settings;
+      useProject.setState({ settings });
+      expect((await formatDocument(view, { explicit: false, onSave: true })).applied).toBe(false);
+      expect(formatter).not.toHaveBeenCalled();
+      useProject.setState({ settings: { ...settings, editor: { ...settings.editor, formatOnSave: true } } });
+      expect((await formatDocument(view, { explicit: false, onSave: true })).applied).toBe(true);
+      expect(view.state.doc.toString()).toBe("SELECT");
+    } finally {
+      view.destroy();
+      useProject.setState(previous);
+    }
+  });
+});
diff --git a/src/editor/lsp/format.ts b/src/editor/lsp/format.ts
index 1e37e1554..061e377c1 100644
--- a/src/editor/lsp/format.ts
+++ b/src/editor/lsp/format.ts
@@ -5,11 +5,14 @@
  * reports "Formatted N lines" with a link to the Reformat File dialog
  * (⌥⇧⌘L: scope and Optimize Imports).
  */
+import { createElement } from "react";
+import styles from "./format.module.css";
 import { indentUnit } from "@codemirror/language";
 import { isolateHistory } from "@codemirror/commands";
 import type { EditorState, Text } from "@codemirror/state";
 import type { EditorView } from "@codemirror/view";
-import { commands } from "@/platform/ipc";
+import { commands, IpcError } from "@/platform/ipc";
+import { notifications } from "@/workbench/contributions";
 import { shortcutLabel } from "@/platform/keymap";
 import { executeAction } from "@/platform/actions";
 import {
@@ -78,14 +81,17 @@ export function formatOptionsOf(state: EditorState): { tabSize: number; insertSp
 
 export async function formatDocument(
   view: EditorView,
-  opts: { explicit: boolean; selectionOnly?: boolean } = { explicit: true },
+  opts: { explicit: boolean; selectionOnly?: boolean; onSave?: boolean } = { explicit: true },
 ): Promise<FormatResult> {
   const result = await format(view, opts);
   if (opts.explicit && result.applied) formattedHint(view, result.lines);
   return result;
 }
 
-async function format(view: EditorView, opts: { explicit: boolean; selectionOnly?: boolean }): Promise<FormatResult> {
+async function format(
+  view: EditorView,
+  opts: { explicit: boolean; selectionOnly?: boolean; onSave?: boolean },
+): Promise<FormatResult> {
   const { project, settings } = useProject.getState();
   const guard = formatGuardOptions(settings);
   const path = docOf(view)?.path;
@@ -95,7 +101,10 @@ async function format(view: EditorView, opts: { explicit: boolean; selectionOnly
     return NOTHING;
   }
   const own = contributedAt<ContributedFormatter>(view.state, CONTRIBUTED_FORMAT, 0);
-  if (own) return applyContributedFormat(view, own, opts, guard);
+  if (own) {
+    if (opts.onSave && !settings?.editor?.formatOnSave) return NOTHING;
+    return applyContributedFormat(view, own, opts, guard);
+  }
   const doc = docOf(view);
   if (!doc || doc.readOnly) return NOTHING;
   // The server formats the backend's copy: let pending keystrokes reach it first.
@@ -107,9 +116,25 @@ async function format(view: EditorView, opts: { explicit: boolean; selectionOnly
   const options = formatOptionsOf(state);
   let edits;
   try {
-    edits = await lspRequest(() => commands.lspFormat(doc.doc, range, options));
+    edits = await lspRequest(() => commands.lspFormat(doc.doc, range, { ...options, onSave: opts.onSave }));
   } catch (e) {
-    reportLspError(view, e, opts.explicit);
+    if (e instanceof IpcError && e.data?.type === "tool" && e.data.tool === "prettier") {
+      if (e.kind === "notFound" && e.data.missing) {
+        await executeAction("tools.promptInstall", { name: "prettier", sticky: !opts.onSave });
+      } else if (e.kind !== "cancelled") {
+        notifications().notify({
+          group: "tools",
+          level: "error",
+          title: tx("Prettier formatting failed"),
+          body:
+            e.kind === "timedOut"
+              ? tx("Prettier formatting timed out")
+              : createElement("span", { className: styles.diagnostics }, e.message),
+          key: `prettier-format-error:${doc.path}`,
+          sticky: false,
+        });
+      }
+    } else reportLspError(view, e, opts.explicit);
     return NOTHING;
   }
   if (view.state.doc !== state.doc) {
@@ -179,7 +204,7 @@ export async function formatLines(view: EditorView, from: number, to: number): P
 function applyContributedFormat(
   view: EditorView,
   format: ContributedFormatter,
-  opts: { explicit: boolean; selectionOnly?: boolean },
+  opts: { explicit: boolean; selectionOnly?: boolean; onSave?: boolean },
   guard: FormatGuardOptions,
 ): FormatResult {
   const state = view.state;
diff --git a/src/editor/lsp/formatErrors.test.tsx b/src/editor/lsp/formatErrors.test.tsx
new file mode 100644
index 000000000..aa21c997f
--- /dev/null
+++ b/src/editor/lsp/formatErrors.test.tsx
@@ -0,0 +1,124 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { act, render, screen } from "@testing-library/react";
+import { EditorState } from "@codemirror/state";
+import { EditorView } from "@codemirror/view";
+import type { IdeError } from "@/bindings";
+import { registerAction } from "@/platform/actions";
+import { _resetI18nForTests, setLocale } from "@/platform/i18n";
+import { IpcError } from "@/platform/ipc";
+import { useProject } from "@/platform/project";
+import { provideNotificationService } from "@/workbench/contributions";
+import { Balloons } from "@/workbench/Notifications";
+import {
+  balloonTimeout,
+  clearNotifications,
+  notificationServiceImpl,
+  useNotifications,
+} from "@/workbench/notificationStore";
+import { formatDocument } from "./format";
+import * as lsp from "./lsp";
+
+const tool = { type: "tool", tool: "prettier", missing: false } as const;
+const views: EditorView[] = [];
+const viewFor = (path = "/project/file.css") => {
+  const view = new EditorView({
+    state: EditorState.create({
+      doc: ".card {",
+      extensions: [lsp.lspDoc.of({ doc: 1, path, language: "css", uiMode: null, readOnly: false })],
+    }),
+  });
+  views.push(view);
+  return view;
+};
+const failWith = (error: IdeError) => vi.spyOn(lsp, "lspRequest").mockRejectedValue(new IpcError(error));
+
+beforeEach(() => {
+  clearNotifications();
+  provideNotificationService(notificationServiceImpl);
+});
+afterEach(() => {
+  views.splice(0).forEach((view) => view.destroy());
+  clearNotifications();
+  vi.restoreAllMocks();
+  _resetI18nForTests();
+});
+
+describe("external formatter errors", () => {
+  it("uses structured missing-tool information to request the shared install prompt", async () => {
+    const prompt = vi.fn();
+    const dispose = registerAction({
+      id: "tools.promptInstall",
+      title: "Install Missing Tool",
+      run: ({ arg }) => prompt(arg),
+    });
+    try {
+      failWith({ kind: "notFound", message: "unrelated diagnostic", data: { ...tool, missing: true } });
+      await formatDocument(viewFor());
+      expect(prompt).toHaveBeenCalledWith({ name: "prettier", sticky: true });
+      await formatDocument(viewFor(), { explicit: false, onSave: true });
+      expect(prompt).toHaveBeenLastCalledWith({ name: "prettier", sticky: false });
+      expect(useNotifications.getState().items).toHaveLength(0);
+    } finally {
+      dispose();
+    }
+  });
+
+  it("does not treat text alone or a broken custom executable as a missing installation", async () => {
+    const prompt = vi.fn();
+    const dispose = registerAction({
+      id: "tools.promptInstall",
+      title: "Install Missing Tool",
+      run: ({ arg }) => prompt(arg),
+    });
+    try {
+      const request = failWith({ kind: "unavailable", message: "Prettier is not installed" });
+      const view = viewFor();
+      await formatDocument(view, { explicit: false });
+      expect(useNotifications.getState().items).toHaveLength(0);
+      request.mockRejectedValue(new IpcError({ kind: "notFound", message: "custom executable missing", data: tool }));
+      await formatDocument(view);
+      expect(prompt).not.toHaveBeenCalled();
+      expect(useNotifications.getState().items).toHaveLength(1);
+    } finally {
+      dispose();
+    }
+  });
+
+  it("keeps stderr untranslated in a Chinese notification and replaces failures per file, including on save", async () => {
+    await setLocale("zh");
+    const previous = useProject.getState().settings;
+    useProject.setState({ settings: null });
+    try {
+      const stderr = "Formatting timed out";
+      failWith({ kind: "invalidInput", message: stderr, data: tool });
+      const view = viewFor();
+      for (let i = 0; i < 3; i++) await formatDocument(view, { explicit: false, onSave: true });
+      const notes = useNotifications.getState().items;
+      expect(notes).toHaveLength(1);
+      expect(notes[0]).toMatchObject({ sticky: false, title: "Prettier 格式化失败" });
+      expect(balloonTimeout(notes[0]!)).toBe(10000);
+      render(<Balloons />);
+      expect(screen.getByRole("alert")).toHaveTextContent(stderr);
+      expect(screen.queryByText("格式化超时")).toBeNull();
+      expect(view.state.doc.toString()).toBe(".card {");
+      await act(async () => {
+        await formatDocument(viewFor("/project/other.css"));
+      });
+      expect(useNotifications.getState().items).toHaveLength(2);
+    } finally {
+      useProject.setState({ settings: previous });
+    }
+  });
+
+  it("localizes the timeout explanation by kind and ignores cancellation", async () => {
+    await setLocale("zh");
+    const request = failWith({ kind: "timedOut", message: "arbitrary backend text", data: tool });
+    const view = viewFor();
+    await formatDocument(view);
+    expect(useNotifications.getState().items[0]).toMatchObject({ body: "Prettier 格式化超时", sticky: false });
+    clearNotifications();
+    request.mockRejectedValue(new IpcError({ kind: "cancelled", message: "cancelled", data: tool }));
+    await formatDocument(view);
+    expect(useNotifications.getState().items).toHaveLength(0);
+  });
+});
diff --git a/src/editor/lsp/navigation.ts b/src/editor/lsp/navigation.ts
index 9dc2d5cdf..7afdda099 100644
--- a/src/editor/lsp/navigation.ts
+++ b/src/editor/lsp/navigation.ts
@@ -1,8 +1,8 @@
 /**
- * Go to declaration / implementation / type declaration (⌘B, ⌥⌘B, ⇧⌘B and
- * ⌘-click with a link underline while ⌘ is held), the multiple-targets
- * chooser, and document highlights (occurrences of the symbol at the caret,
- * plus the sticky find.highlightUsages variant).
+ * Go to declaration / implementation / type declaration (⌘B, ⌥⌘B, ⇧⌘B,
+ * ⌘-click with a link underline while ⌘ is held, and a plain middle-button
+ * click), the multiple-targets chooser, and document highlights (occurrences
+ * of the symbol at the caret, plus the sticky find.highlightUsages variant).
  */
 import { EditorSelection, Prec, StateEffect, StateField, type Extension, type Text } from "@codemirror/state";
 import {
@@ -489,7 +489,7 @@ const linkPlugin = ViewPlugin.fromClass(
         this.show(false);
       },
       mousedown(e, view) {
-        if (e.button !== 0) return false;
+        if (e.button !== 0 && e.button !== 1) return false;
         if (
           dispatchMouseShortcut(e, () => {
             const pos = view.posAtCoords({ x: e.clientX, y: e.clientY }, false);
@@ -502,7 +502,8 @@ const linkPlugin = ViewPlugin.fromClass(
           e.preventDefault();
           return true;
         }
-        if (!isNavigationGesture(e)) return false;
+        // IDEA parity: middle button navigates on a plain click, without the modifier.
+        if (e.button === 1 ? e.metaKey || e.ctrlKey || e.altKey || e.shiftKey : !isNavigationGesture(e)) return false;
         const pos = view.posAtCoords({ x: e.clientX, y: e.clientY }, false);
         if (pos == null) return false;
         e.preventDefault();
diff --git a/src/editor/lsp/navigationMouse.test.ts b/src/editor/lsp/navigationMouse.test.ts
index 3940c61df..5ec3b9d53 100644
--- a/src/editor/lsp/navigationMouse.test.ts
+++ b/src/editor/lsp/navigationMouse.test.ts
@@ -94,6 +94,14 @@ describe("mouse navigation", () => {
     expect(lspGoto).toHaveBeenCalledExactlyOnceWith(1, { line: 0, col: 9 }, "definition");
   });
 
+  it("opens the definition from a plain middle-button click", async () => {
+    const event = click({ button: 1 });
+    await vi.waitFor(() => expect(openFile).toHaveBeenCalledOnce());
+    expect(lspGoto).toHaveBeenCalledExactlyOnceWith(1, { line: 0, col: 9 }, "definition");
+    expect(view.state.selection.main.head).toBe(9);
+    expect(event.defaultPrevented).toBe(true);
+  });
+
   it.each([
     { button: 1, metaKey: true, altKey: true },
     { button: 2, metaKey: true, altKey: true },
diff --git a/src/editor/lsp/rename.ts b/src/editor/lsp/rename.ts
index 48fb7ec45..aaeed7547 100644
--- a/src/editor/lsp/rename.ts
+++ b/src/editor/lsp/rename.ts
@@ -15,12 +15,14 @@ import type { EditorView } from "@codemirror/view";
 import {
   commands,
   isCancelled,
+  isNoServer,
   nextRequestId,
   unavailableText,
   type Pos,
   type RequestId,
   type WorkspaceEdit,
 } from "@/platform/ipc";
+import { executeAction } from "@/platform/actions";
 import { whenSynced, type EditorDocContext } from "@/editor/api";
 import { structure } from "@/editor/structure";
 import { docOf, incompleteNote, isUnavailable, lspRequest, reportLspError } from "./lsp";
@@ -78,7 +80,10 @@ export async function startRename(view: EditorView) {
     range = await lspRequest(() => commands.lspPrepareRename(doc.doc, pos));
   } catch (e) {
     if (isCancelled(e)) return;
-    if (!(await startSyntaxRename(view, doc, pos, e))) reportLspError(view, e, true);
+    if (await startSyntaxRename(view, doc, pos, e)) return;
+    // No server covers this file (a plain text file): Shift+F6 renames the file, like IDEA.
+    if (isNoServer(e) && (await executeAction("project.rename"))) return;
+    reportLspError(view, e, true);
     return;
   }
   if (!range) {
diff --git a/src/editor/lsp/syntaxFallback.test.ts b/src/editor/lsp/syntaxFallback.test.ts
index 2b811ad5d..366cbb6da 100644
--- a/src/editor/lsp/syntaxFallback.test.ts
+++ b/src/editor/lsp/syntaxFallback.test.ts
@@ -30,6 +30,13 @@ vi.mock("@/platform/ipc", async (orig) => {
   return { ...actual, isTauri: () => true, commands: { ...actual.commands, ...cmd } };
 });
 
+const executeAction = vi.hoisted(() => vi.fn());
+vi.mock("@/platform/actions", async (orig) => {
+  const actual = await orig<typeof import("@/platform/actions")>();
+  executeAction.mockImplementation(actual.executeAction);
+  return { ...actual, executeAction };
+});
+
 const openFile = vi.fn(async () => {});
 const { provideEditorService } = await import("@/workbench/contributions");
 provideEditorService({ openFile } as never);
@@ -488,6 +495,34 @@ describe("rename wiring", () => {
     });
   });
 
+  it("renames the file itself when no server covers it (a plain text file)", async () => {
+    cmd.lspPrepareRename.mockReturnValueOnce(
+      Promise.resolve({
+        status: "error",
+        error: { kind: "unavailable", message: "no running language server supports rename" } as IdeError,
+      }),
+    );
+    cmd.syntaxSupport.mockReturnValueOnce(ok({ tree: false, locals: false }));
+    executeAction.mockResolvedValueOnce(true);
+    const view = editor("# notes", "markdown", 2);
+    await startRename(view);
+    expect(executeAction).toHaveBeenCalledWith("project.rename");
+    expect(document.querySelector(".cm-lsp-hint")).toBeNull();
+  });
+
+  it("keeps the hint when a server runs but lacks rename (no file fallback)", async () => {
+    cmd.lspPrepareRename.mockReturnValueOnce(
+      Promise.resolve({
+        status: "error",
+        error: { kind: "unavailable", message: "jdtls doesn't support rename" } as IdeError,
+      }),
+    );
+    const view = editor("class A {}", "java", 6);
+    await startRename(view);
+    expect(executeAction).not.toHaveBeenCalledWith("project.rename");
+    expect(document.querySelector(".cm-lsp-hint")?.textContent).toContain("jdtls doesn't support rename");
+  });
+
   it("respects a server refusal over valid code, but falls back over broken code", async () => {
     cmd.lspPrepareRename.mockReturnValueOnce(ok(null));
     const view = editor("const x = 1;", "typescript", 6);
diff --git a/src/features/app/__tests__/host.test.ts b/src/features/app/__tests__/host.test.ts
new file mode 100644
index 000000000..27f7d38ee
--- /dev/null
+++ b/src/features/app/__tests__/host.test.ts
@@ -0,0 +1,51 @@
+import { beforeEach, expect, it, vi } from "vitest";
+import type { BuildInfo } from "@/platform/ipc";
+
+const { appBuildInfo, isTauri } = vi.hoisted(() => ({ appBuildInfo: vi.fn(), isTauri: vi.fn() }));
+vi.mock("@/platform/ipc", () => ({ commands: { appBuildInfo }, isTauri }));
+
+const build: BuildInfo = {
+  version: "0.1.32",
+  build: "dev",
+  profile: "debug",
+  os: "windows",
+  arch: "x86_64",
+  tauri: "2.11.3",
+  updates: false,
+};
+
+beforeEach(() => {
+  vi.resetModules();
+  appBuildInfo.mockReset();
+  isTauri.mockReturnValue(true);
+});
+
+it("retries after a rejected request and caches the successful build info", async () => {
+  appBuildInfo.mockRejectedValueOnce(new Error("Project is not trusted")).mockResolvedValueOnce(build);
+  const { buildInfo, hostOs } = await import("../host");
+
+  const first = buildInfo();
+  expect(buildInfo()).toBe(first);
+  await expect(first).resolves.toBeNull();
+  await expect(hostOs()).resolves.toBe("windows");
+  await expect(buildInfo()).resolves.toBe(build);
+  expect(appBuildInfo).toHaveBeenCalledTimes(2);
+});
+
+it("shares an in-flight successful request", async () => {
+  let resolve!: (value: BuildInfo) => void;
+  appBuildInfo.mockReturnValue(new Promise<BuildInfo>((done) => (resolve = done)));
+  const { buildInfo } = await import("../host");
+  const first = buildInfo();
+  expect(buildInfo()).toBe(first);
+  expect(appBuildInfo).toHaveBeenCalledTimes(1);
+  resolve(build);
+  await expect(first).resolves.toBe(build);
+});
+
+it("does not invoke the backend outside Tauri", async () => {
+  isTauri.mockReturnValue(false);
+  const { buildInfo } = await import("../host");
+  await expect(buildInfo()).resolves.toBeNull();
+  expect(appBuildInfo).not.toHaveBeenCalled();
+});
diff --git a/src/features/app/host.ts b/src/features/app/host.ts
index 649365e98..4e1fdacdb 100644
--- a/src/features/app/host.ts
+++ b/src/features/app/host.ts
@@ -13,7 +13,12 @@ function normalize(os: string): HostOs {
 let info: Promise<BuildInfo | null> | null = null;
 
 export function buildInfo(): Promise<BuildInfo | null> {
-  info ??= isTauri() ? commands.appBuildInfo().catch(() => null) : Promise.resolve(null);
+  info ??= isTauri()
+    ? commands.appBuildInfo().catch(() => {
+        info = null;
+        return null;
+      })
+    : Promise.resolve(null);
   return info;
 }
 
diff --git a/src/features/debugger/__tests__/actions.test.ts b/src/features/debugger/__tests__/actions.test.ts
index 0fe45b753..295b6944e 100644
--- a/src/features/debugger/__tests__/actions.test.ts
+++ b/src/features/debugger/__tests__/actions.test.ts
@@ -268,3 +268,23 @@ describe("debugger actions (IDEA parity)", () => {
     expect(useOverlays.getState().evaluate?.expression).toBe("total = order.items\nfor i in x:");
   });
 });
+
+describe("output class breakpoint restrictions", () => {
+  it.each([
+    "debug.toggleBreakpoint",
+    "debug.toggleTemporaryBreakpoint",
+    "debug.toggleMethodBreakpoint",
+    "debug.toggleFieldWatchpoint",
+    "debug.runToCursor",
+    "debug.forceRunToCursor",
+  ])("blocks %s for a source-less output class", async (id) => {
+    paused();
+    const path = "file:///p/target/classes/p/C.class";
+    caret(path, "java", "class C {\n int n;\n void run() {}\n}", 2);
+    await executeAction(id);
+    expect(breakpointsOf(path)).toHaveLength(0);
+    expect(useSpecialBreakpoints.getState().methods).toHaveLength(0);
+    expect(useSpecialBreakpoints.getState().fields).toHaveLength(0);
+    expect(ipc.debugRunTo).not.toHaveBeenCalled();
+  });
+});
diff --git a/src/features/debugger/__tests__/editor.test.ts b/src/features/debugger/__tests__/editor.test.ts
index 57d96067d..b975cca61 100644
--- a/src/features/debugger/__tests__/editor.test.ts
+++ b/src/features/debugger/__tests__/editor.test.ts
@@ -53,6 +53,32 @@ describe("breakpoint gutter", () => {
   });
 });
 
+describe("output class gutter", () => {
+  it("disables ordinary, temporary and logging breakpoints and explains why", () => {
+    loadBreakpoints("/proj");
+    const path = "file:///proj/target/classes/C.class";
+    const view = new EditorView({
+      state: EditorState.create({
+        doc: "class C {}",
+        extensions: [
+          lineNumbers(),
+          breakpointGutter({ ...ctx, path, language: "java", readOnly: true, virtual: true }),
+        ],
+      }),
+      parent: document.body,
+    });
+    views.push(view);
+    const cell = view.dom.querySelector(".cm-lineNumbers .cm-gutterElement")!;
+    cell.dispatchEvent(new MouseEvent("mouseover", { bubbles: true }));
+    expect(cell.closest(".cm-gutters")?.getAttribute("title")).toMatch(/output classes without source code/);
+    for (const modifier of [{}, { altKey: true }, { shiftKey: true }]) {
+      cell.dispatchEvent(new MouseEvent("mousedown", { bubbles: true, button: 0, ...modifier }));
+      cell.dispatchEvent(new MouseEvent("mouseup", { bubbles: true, button: 0, ...modifier }));
+    }
+    expect(breakpointsOf(path)).toHaveLength(0);
+  });
+});
+
 describe("breakpoint look", () => {
   it("shows the verified icon only while a session has bound it", () => {
     const b = { id: "1", line: 0, enabled: true, condition: null, logMessage: null, hitCondition: null };
diff --git a/src/features/debugger/actions.ts b/src/features/debugger/actions.ts
index 78a08fe4e..3112affc7 100644
--- a/src/features/debugger/actions.ts
+++ b/src/features/debugger/actions.ts
@@ -5,6 +5,7 @@ import { downloadJdkActions } from "@/platform/jdk";
 import { useProject } from "@/platform/project";
 import { activeEditor } from "@/editor/api";
 import { maybeEditorService, notifications, showStatusInfo, toolWindowService } from "@/workbench/contributions";
+import { classFileBreakpointReason } from "@/platform/classFiles";
 import { canPlaceBreakpoint } from "./breakpoints/languages";
 import {
   removeAllBreakpoints,
@@ -75,10 +76,18 @@ function pausedTarget(): { s: DebugSession; thread: number } | null {
   return thread == null ? null : { s, thread };
 }
 
+function breakpointPathAllowed(path: string): boolean {
+  const reason = classFileBreakpointReason(path);
+  if (!reason) return true;
+  showStatusInfo(tx(reason));
+  return false;
+}
+
 /** Run to Cursor at `line` (0-based) of `path` in the paused session. */
 export function runToLine(path: string, line: number) {
   const t = pausedTarget();
-  if (t) void report("Run to Cursor failed", call(commands.debugRunTo(t.s.id, t.thread, path, line, false)));
+  if (t && breakpointPathAllowed(path))
+    void report("Run to Cursor failed", call(commands.debugRunTo(t.s.id, t.thread, path, line, false)));
 }
 
 function notSupported(what: string, s: DebugSession) {
@@ -518,7 +527,7 @@ export function registerDebugActions(): () => void {
       run: () => {
         const t = pausedTarget();
         const c = cursor();
-        if (t && c)
+        if (t && c && breakpointPathAllowed(c.path))
           void report("Run to Cursor failed", call(commands.debugRunTo(t.s.id, t.thread, c.path, c.line, false)));
       },
     },
@@ -532,7 +541,7 @@ export function registerDebugActions(): () => void {
       run: () => {
         const t = pausedTarget();
         const c = cursor();
-        if (t && c)
+        if (t && c && breakpointPathAllowed(c.path))
           void report("Force Run to Cursor failed", call(commands.debugRunTo(t.s.id, t.thread, c.path, c.line, true)));
       },
     },
@@ -543,7 +552,7 @@ export function registerDebugActions(): () => void {
       icon: "breakpoint",
       run: () => {
         const c = cursor();
-        if (!c) return;
+        if (!c || !breakpointPathAllowed(c.path)) return;
         const exists = useBreakpoints.getState().byFile[c.path]?.some((b) => b.line === c.line);
         const language = activeEditor()?.ctx.language ?? "";
         if (!exists && !canPlaceBreakpoint(language)) {
@@ -568,7 +577,8 @@ export function registerDebugActions(): () => void {
       description: "A line breakpoint that is removed after it is hit",
       run: () => {
         const c = cursor();
-        if (c && canPlaceBreakpoint(activeEditor()?.ctx.language ?? "")) toggleTemporaryBreakpoint(c.path, c.line);
+        if (c && breakpointPathAllowed(c.path) && canPlaceBreakpoint(activeEditor()?.ctx.language ?? "", c.path))
+          toggleTemporaryBreakpoint(c.path, c.line);
       },
     },
     {
@@ -579,7 +589,7 @@ export function registerDebugActions(): () => void {
       run: () => {
         const ed = activeEditor();
         const c = cursor();
-        if (!ed || !c) return;
+        if (!ed || !c || !breakpointPathAllowed(c.path)) return;
         const existing = specialAt(c.path).find((b) => b.kind === "method" && b.line === c.line);
         const method = methodAt(ed.ctx.language, ed.view.state.doc.toString(), c.line);
         if (!existing && !method) {
@@ -602,7 +612,7 @@ export function registerDebugActions(): () => void {
       run: () => {
         const ed = activeEditor();
         const c = cursor();
-        if (!ed || !c) return;
+        if (!ed || !c || !breakpointPathAllowed(c.path)) return;
         const existing = specialAt(c.path).find((b) => b.kind === "field" && b.line === c.line);
         const field = fieldAt(ed.ctx.language, ed.view.state.doc.toString(), c.line);
         if (!existing && !field) {
diff --git a/src/features/debugger/breakpoints/languages.ts b/src/features/debugger/breakpoints/languages.ts
index 1496645db..e532b40d3 100644
--- a/src/features/debugger/breakpoints/languages.ts
+++ b/src/features/debugger/breakpoints/languages.ts
@@ -3,6 +3,7 @@
  * when off, new line breakpoints go only into files of languages that have a
  * debug adapter (`languages/*.toml` `[debugger]`).
  */
+import { classFileBreakpointReason } from "@/platform/classFiles";
 import { commands, isTauri } from "@/platform/ipc";
 import { workflowSettings } from "@/platform/workflowSettings";
 
@@ -22,7 +23,8 @@ function load() {
 }
 
 /** Whether a new breakpoint may be placed in a file of `language`. */
-export function canPlaceBreakpoint(language: string): boolean {
+export function canPlaceBreakpoint(language: string, path = ""): boolean {
+  if (classFileBreakpointReason(path)) return false;
   if (workflowSettings().debugger.breakpointsAnyFile) return true;
   load();
   // Until the language list is known, don't block anything.
diff --git a/src/features/debugger/editor/breakpointGutter.ts b/src/features/debugger/editor/breakpointGutter.ts
index 075dc954b..ada2140ce 100644
--- a/src/features/debugger/editor/breakpointGutter.ts
+++ b/src/features/debugger/editor/breakpointGutter.ts
@@ -15,6 +15,9 @@ import {
   updateBreakpoint,
   useBreakpoints,
 } from "../breakpoints/store";
+import { classFileBreakpointReason } from "@/platform/classFiles";
+import { tx } from "@/platform/i18n";
+import { showStatusInfo } from "@/workbench/contributions";
 import { canPlaceBreakpoint } from "../breakpoints/languages";
 import {
   removeSpecial,
@@ -129,6 +132,31 @@ function inBreakpointArea(e: MouseEvent): boolean {
 }
 
 export function breakpointGutter(ctx: EditorDocContext): Extension {
+  const reason = classFileBreakpointReason(ctx.path);
+  if (reason) {
+    const message = tx(reason);
+    return ViewPlugin.fromClass(
+      class {
+        constructor(readonly view: EditorView) {
+          view.dom.addEventListener("mouseover", this.hover);
+          view.dom.addEventListener("mousedown", this.down, true);
+        }
+        hover = (e: MouseEvent) => {
+          if (inBreakpointArea(e)) (e.target as HTMLElement).closest(".cm-gutters")?.setAttribute("title", message);
+        };
+        down = (e: MouseEvent) => {
+          if (!inBreakpointArea(e)) return;
+          showStatusInfo(message);
+        };
+        destroy() {
+          this.view.dom.removeEventListener("mouseover", this.hover);
+          this.view.dom.removeEventListener("mousedown", this.down, true);
+          const gutters = this.view.dom.querySelector(".cm-gutters");
+          if (gutters?.getAttribute("title") === message) gutters.removeAttribute("title");
+        }
+      },
+    );
+  }
   const path = ctx.path;
   const field = StateField.define<RangeSet<BreakpointMarker>>({
     create: (state) => buildMarkers(state, path),
diff --git a/src/features/debugger/editor/runToCursor.ts b/src/features/debugger/editor/runToCursor.ts
index f1f3ca7d2..1db51c42c 100644
--- a/src/features/debugger/editor/runToCursor.ts
+++ b/src/features/debugger/editor/runToCursor.ts
@@ -3,6 +3,7 @@
  * line shows a small button left of its text that runs to that line (Resume on
  * the execution line itself). Settings › Debugger › "Show inlay Run to Cursor popup".
  */
+import { classFileBreakpointReason } from "@/platform/classFiles";
 import type { Extension } from "@codemirror/state";
 import { EditorView, ViewPlugin } from "@codemirror/view";
 import type { EditorDocContext } from "@/editor/api";
@@ -30,7 +31,7 @@ export function hoveredLine(
 }
 
 export function runToCursorInlay(ctx: EditorDocContext): Extension {
-  if (ctx.virtual) return [];
+  if (classFileBreakpointReason(ctx.path) || (ctx.virtual && !ctx.path.startsWith("jdt:"))) return [];
   const path = ctx.path;
   return ViewPlugin.fromClass(
     class {
diff --git a/src/features/project-tree/contextMenu.test.ts b/src/features/project-tree/contextMenu.test.ts
index 622ddf3b0..d3f18a6d5 100644
--- a/src/features/project-tree/contextMenu.test.ts
+++ b/src/features/project-tree/contextMenu.test.ts
@@ -40,6 +40,7 @@ const OTHER_ACTIONS = [
   "localHistory.putLabel",
   "diff.compareWith",
   "diff.compareFiles",
+  "diff.compareDirectories",
   "vcs.commit",
   "vcs.addToVcs",
   "vcs.annotate",
@@ -75,6 +76,14 @@ afterEach(() => {
 });
 
 describe("project view context menu", () => {
+  it("offers directory comparison only for two folders and Compare With for a single folder", () => {
+    expect(labels(contextMenuItems([node("/p/left", true), node("/p/right", true)]))).toContain("Compare Directories");
+    expect(labels(contextMenuItems([node("/p/left", true)]))).toContain("Compare With…");
+    const mixed = labels(contextMenuItems([node("/p/left", true), node("/p/a.txt")]));
+    for (const label of ["Compare Directories", "Compare Files", "Compare With…"]) expect(mixed).not.toContain(label);
+    expect(labels(contextMenuItems([node("/p/a.txt"), node("/p/b.txt")]))).toContain("Compare Files");
+  });
+
   it("follows IDEA's order for a file", () => {
     const items = contextMenuItems([node(`${ROOT}/src/a.py`)]);
     expect(labels(items)).toEqual([
@@ -161,7 +170,7 @@ describe("project view context menu", () => {
     const l = labels(contextMenuItems([node(`${ROOT}/src`, true)]));
     expect(l).toContain("Mark Directory as");
     expect(sub(contextMenuItems([node(`${ROOT}/src`, true)]), "Refactor")).toContain("Move Directory…");
-    for (const fileOnly of ["Find Usages", "Reformat Code", "Optimize Imports", "Compare With…", "Run 'a'"])
+    for (const fileOnly of ["Find Usages", "Reformat Code", "Optimize Imports", "Run 'a'"])
       expect(l).not.toContain(fileOnly);
   });
 
diff --git a/src/features/project-tree/contextMenu.ts b/src/features/project-tree/contextMenu.ts
index 1b35cf483..9775c9b4c 100644
--- a/src/features/project-tree/contextMenu.ts
+++ b/src/features/project-tree/contextMenu.ts
@@ -361,7 +361,17 @@ export function contextMenuItems(nodes: ProjectNode[]): MenuItem[] {
     );
   }
 
-  // IDEA: Compare With… (one file) / Compare Files (two files).
+  // Compare selections of the same kind; mixed file/folder selections cannot apply.
+  const compareArg = single?.dir ? { path: single.path, directory: true } : single?.path;
+  if (nodes.length === 2 && nodes.every((n) => n.dir && !n.placeholder))
+    push(
+      delegated(
+        "diff.compareDirectories",
+        nodes.map((n) => n.path),
+        "Compare Directories",
+        { icon: "diff" },
+      ),
+    );
   if (files.length === 2 && nodes.length === 2)
     push(
       delegated(
@@ -371,9 +381,9 @@ export function contextMenuItems(nodes: ProjectNode[]): MenuItem[] {
         { icon: "diff" },
       ),
     );
-  else if (singleFile)
+  else if (single && !single.placeholder)
     push(
-      delegated("diff.compareWith", singleFile.path, "Compare With…", {
+      delegated("diff.compareWith", compareArg, "Compare With…", {
         icon: "diff",
         shortcut: keyLabel("project.compareWith"),
       }),
diff --git a/src/features/search/__tests__/dialogs.test.tsx b/src/features/search/__tests__/dialogs.test.tsx
index 3e10bacd2..202c6dffe 100644
--- a/src/features/search/__tests__/dialogs.test.tsx
+++ b/src/features/search/__tests__/dialogs.test.tsx
@@ -1,12 +1,17 @@
-import { afterEach, describe, expect, it, vi } from "vitest";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import { act, fireEvent, render, screen, within } from "@testing-library/react";
 import { registerAction } from "@/platform/actions";
 import type { SeDeps } from "../everywhere/controller";
 
+const defaultFindFiles: SeDeps["findFiles"] = async (q) =>
+  q ? [{ path: "/p/src/OrderController.kt", relPath: "src/OrderController.kt", score: 1, indices: [4, 5, 6] }] : [];
+let findFiles = defaultFindFiles;
+let findSymbols: SeDeps["findSymbols"] = async () => [];
+let settings: NonNullable<SeDeps["settings"]> = async () => [];
 const fakeDeps = (): SeDeps => ({
-  findFiles: async (q) =>
-    q ? [{ path: "/p/src/OrderController.kt", relPath: "src/OrderController.kt", score: 1, indices: [4, 5, 6] }] : [],
-  findSymbols: async () => [],
+  findFiles: (...args) => findFiles(...args),
+  findSymbols: (...args) => findSymbols(...args),
+  settings: () => settings(),
   searchText: async () => {},
   cancel: () => {},
   nextRequestId: () => 1,
@@ -18,6 +23,11 @@ const fakeDeps = (): SeDeps => ({
   now: () => 0,
 });
 
+vi.mock("../common/open", async (orig) => ({
+  ...(await orig<typeof import("../common/open")>()),
+  openLocation: vi.fn(async () => {}),
+}));
+
 vi.mock("../everywhere/deps", () => ({
   ipcDeps: () => fakeDeps(),
   loadLanguages: async () => [
@@ -42,6 +52,12 @@ vi.mock("../find/windowStore", async (orig) => ({
   }),
 }));
 
+const contributions = await import("@/workbench/contributions");
+const { commands } = await import("@/platform/ipc");
+const { RecentPopupsOverlay } = await import("../recent/RecentPopups");
+const { showRecentPopup, hideRecentPopup, useRecentPopup } = await import("../recent/store");
+const { openLocation } = await import("../common/open");
+const { usePlatform } = await import("@/platform/platformInfo");
 const { allActions } = await import("@/platform/actions");
 (globalThis as unknown as { __actions: typeof allActions }).__actions = allActions;
 const { SearchEverywhereOverlay } = await import("../everywhere/SearchEverywhere");
@@ -52,10 +68,18 @@ const { showFindPopup, hideFindPopup } = await import("../find/store");
 
 const tick = () => act(() => new Promise((r) => setTimeout(r, 100)));
 
+beforeEach(() => {
+  findFiles = defaultFindFiles;
+  findSymbols = async () => [];
+  settings = async () => [];
+  vi.mocked(openLocation).mockClear();
+});
+
 afterEach(() => {
   act(() => {
     hideSearchEverywhere();
     hideFindPopup();
+    hideRecentPopup();
   });
 });
 
@@ -203,6 +227,254 @@ describe("Search Everywhere dialog", () => {
   });
 });
 
+const duplicateFiles: Awaited<ReturnType<SeDeps["findFiles"]>> = ["one", "two", "three"].map((dir) => ({
+  path: `/p/${dir}/index.ts`,
+  relPath: `${dir}/index.ts`,
+  score: 1,
+  indices: [0, 1, 2, 3, 4],
+}));
+const resultOptions = () => within(document.getElementById("se-results")!).getAllByRole("option");
+const selectedOptions = () => resultOptions().filter((r) => r.getAttribute("aria-selected") === "true");
+async function showDuplicateFiles() {
+  findFiles = async () => duplicateFiles;
+  render(<SearchEverywhereOverlay />);
+  act(() => showSearchEverywhere("files", { query: "index" }));
+  await tick();
+  return screen.getByLabelText("Search query");
+}
+function clickOption(index: number, modifiers = {}) {
+  const row = resultOptions()[index]!;
+  fireEvent.mouseDown(row, modifiers);
+  fireEvent.click(row, modifiers);
+}
+
+describe("Search Everywhere multi-selection", () => {
+  it("extends, shrinks, crosses the anchor and clamps Shift selection; plain arrows select one", async () => {
+    const input = await showDuplicateFiles();
+    const key = (key: string, shiftKey = true) => fireEvent.keyDown(input, { key, shiftKey });
+    key("ArrowDown", false);
+    key("ArrowDown");
+    expect(selectedOptions()).toEqual(resultOptions().slice(1));
+    key("ArrowDown");
+    expect(selectedOptions()).toHaveLength(2);
+    key("ArrowUp");
+    expect(selectedOptions()).toEqual([resultOptions()[1]]);
+    key("ArrowUp");
+    expect(selectedOptions()).toEqual(resultOptions().slice(0, 2));
+    key("ArrowDown", false);
+    expect(selectedOptions()).toEqual([resultOptions()[1]]);
+    expect(screen.getByRole("listbox", { name: "Results" })).toHaveAttribute("aria-multiselectable", "true");
+  });
+
+  it("Shift-click selects a range without opening; an ordinary click opens just that file", async () => {
+    await showDuplicateFiles();
+    clickOption(2, { shiftKey: true });
+    expect(selectedOptions()).toHaveLength(3);
+    expect(openLocation).not.toHaveBeenCalled();
+    expect(useSearchEverywhere.getState().open).toBe(true);
+    clickOption(1);
+    await tick();
+    expect(openLocation).toHaveBeenCalledExactlyOnceWith("/p/two/index.ts", null, { side: false });
+    expect(useSearchEverywhere.getState().open).toBe(false);
+  });
+
+  it.each(["macos", "windows", "linux"] as const)("uses the primary modifier to toggle a row on %s", async (os) => {
+    const previous = usePlatform.getState().os;
+    usePlatform.setState({ os });
+    try {
+      const input = await showDuplicateFiles();
+      const modifier = os === "macos" ? { metaKey: true } : { ctrlKey: true };
+      clickOption(2, modifier);
+      expect(selectedOptions()).toEqual([resultOptions()[0], resultOptions()[2]]);
+      clickOption(0, modifier);
+      expect(selectedOptions()).toEqual([resultOptions()[2]]);
+      expect(openLocation).not.toHaveBeenCalled();
+      fireEvent.keyDown(input, { key: "Enter" });
+      await tick();
+      expect(openLocation).toHaveBeenCalledExactlyOnceWith("/p/three/index.ts", null, { side: false });
+    } finally {
+      usePlatform.setState({ os: previous });
+    }
+  });
+
+  it("awaits each open in list order, keeps tabs and restores an upward range's lead", async () => {
+    const input = await showDuplicateFiles();
+    fireEvent.keyDown(input, { key: "ArrowDown" });
+    fireEvent.keyDown(input, { key: "ArrowDown" });
+    fireEvent.keyDown(input, { key: "ArrowUp", shiftKey: true });
+    let finishFirst!: () => void;
+    vi.mocked(openLocation).mockImplementationOnce(
+      () =>
+        new Promise((r) => {
+          finishFirst = r;
+        }),
+    );
+    fireEvent.keyDown(input, { key: "Enter" });
+    await tick();
+    expect(openLocation).toHaveBeenCalledTimes(1);
+    expect(useSearchEverywhere.getState().open).toBe(true);
+    fireEvent.keyDown(input, { key: "Enter" });
+    expect(openLocation).toHaveBeenCalledTimes(1);
+    expect(openLocation).toHaveBeenNthCalledWith(1, "/p/two/index.ts", null, {
+      preview: false,
+      focus: false,
+      side: false,
+    });
+    await act(async () => finishFirst());
+    await tick();
+    expect(vi.mocked(openLocation).mock.calls).toEqual([
+      ["/p/two/index.ts", null, { preview: false, focus: false, side: false }],
+      ["/p/three/index.ts", null, { preview: false, focus: false, side: false }],
+      ["/p/two/index.ts", null, { preview: false, focus: true, side: false }],
+    ]);
+    expect(useSearchEverywhere.getState().open).toBe(false);
+  });
+
+  it("resets selection immediately on query changes and tab switches", async () => {
+    const input = await showDuplicateFiles();
+    clickOption(2, { shiftKey: true });
+    fireEvent.change(input, { target: { value: "index.t" } });
+    expect(selectedOptions()).toHaveLength(1);
+    await tick();
+    clickOption(2, { shiftKey: true });
+    fireEvent.click(screen.getByRole("tab", { name: "All" }));
+    expect(selectedOptions()).toHaveLength(1);
+    await tick();
+    expect(selectedOptions()).toHaveLength(1);
+  });
+
+  it.each(["classes", "symbols"] as const)("opens selected %s at their positions", async (tab) => {
+    findSymbols = async () =>
+      ["First", "Second"].map((name, line) => ({
+        name,
+        kind: tab === "classes" ? "class" : "function",
+        container: null,
+        path: `/p/${name}.ts`,
+        relPath: `${name}.ts`,
+        score: 1,
+        indices: [0],
+        range: { start: { line, col: 2 }, end: { line, col: 5 } },
+      }));
+    render(<SearchEverywhereOverlay />);
+    act(() => showSearchEverywhere(tab, { query: "s" }));
+    await tick();
+    const input = screen.getByLabelText("Search query");
+    fireEvent.keyDown(input, { key: "ArrowDown", shiftKey: true });
+    fireEvent.keyDown(input, { key: "Enter" });
+    await tick();
+    expect(openLocation).toHaveBeenNthCalledWith(
+      1,
+      "/p/First.ts",
+      { line: 0, col: 2 },
+      expect.objectContaining({ preview: false }),
+    );
+    expect(openLocation).toHaveBeenNthCalledWith(
+      2,
+      "/p/Second.ts",
+      { line: 1, col: 2 },
+      expect.objectContaining({ preview: false }),
+    );
+  });
+
+  it("ignores actions and settings in a mixed selection even when the lead is an action", async () => {
+    const run = vi.fn();
+    const dispose = registerAction({ id: "test.index", title: "Index", category: "Test", run });
+    findFiles = async () => duplicateFiles.slice(0, 2);
+    settings = async () => [{ pageId: "editor", title: "Index", path: ["Editor"] }];
+    render(<SearchEverywhereOverlay />);
+    act(() => showSearchEverywhere("all", { query: "index" }));
+    await tick();
+    const input = screen.getByLabelText("Search query");
+    const count = resultOptions().length;
+    for (let i = 1; i < count; i++) fireEvent.keyDown(input, { key: "ArrowDown" });
+    for (let i = 1; i < count; i++) fireEvent.keyDown(input, { key: "ArrowUp", shiftKey: true });
+    expect(selectedOptions()).toHaveLength(count);
+    fireEvent.keyDown(input, { key: "Enter" });
+    await tick();
+    expect(run).not.toHaveBeenCalled();
+    expect(vi.mocked(openLocation).mock.calls.map((c) => c[0])).toEqual([
+      "/p/one/index.ts",
+      "/p/two/index.ts",
+      "/p/two/index.ts",
+    ]);
+    dispose();
+  });
+
+  it("does not execute a multi-selection containing only actions", async () => {
+    const run = vi.fn();
+    const disposers = ["One", "Two"].map((name) =>
+      registerAction({ id: `test.index${name}`, title: `Index ${name}`, run }),
+    );
+    render(<SearchEverywhereOverlay />);
+    act(() => showSearchEverywhere("actions", { query: "index" }));
+    await tick();
+    const input = screen.getByLabelText("Search query");
+    fireEvent.keyDown(input, { key: "ArrowDown", shiftKey: true });
+    fireEvent.keyDown(input, { key: "Enter" });
+    await tick();
+    expect(run).not.toHaveBeenCalled();
+    expect(openLocation).not.toHaveBeenCalled();
+    disposers.forEach((d) => d());
+  });
+});
+
+describe("Recent Files multi-selection", () => {
+  async function showFiles() {
+    vi.spyOn(commands, "recentFiles").mockResolvedValue({ status: "ok", data: duplicateFiles.map((f) => f.path) });
+    render(<RecentPopupsOverlay />);
+    act(() => showRecentPopup("files"));
+    await tick();
+    return screen.getByLabelText("Filter recent files");
+  }
+  const options = () => within(screen.getByRole("listbox", { name: "Recent files" })).getAllByRole("option");
+  afterEach(() => vi.restoreAllMocks());
+
+  it("extends and shrinks a keyboard range, then opens its files in order", async () => {
+    const input = await showFiles();
+    fireEvent.keyDown(input, { key: "ArrowDown" });
+    fireEvent.keyDown(input, { key: "ArrowUp", shiftKey: true });
+    expect(options().filter((r) => r.getAttribute("aria-selected") === "true")).toHaveLength(2);
+    fireEvent.keyDown(input, { key: "Enter" });
+    await tick();
+    expect(vi.mocked(openLocation).mock.calls.map((c) => c[0])).toEqual([
+      "/p/one/index.ts",
+      "/p/two/index.ts",
+      "/p/one/index.ts",
+    ]);
+    expect(useRecentPopup.getState().open).toBeNull();
+  });
+
+  it("starts a range at the initially selected previous file", async () => {
+    vi.spyOn(contributions, "maybeEditorService").mockReturnValue({
+      activePath: () => "/p/one/index.ts",
+    } as import("@/workbench/contributions").EditorService);
+    const input = await showFiles();
+    expect(options()[1]).toHaveAttribute("aria-selected", "true");
+    fireEvent.keyDown(input, { key: "ArrowDown", shiftKey: true });
+    expect(options()[0]).toHaveAttribute("aria-selected", "false");
+    expect(options()[1]).toHaveAttribute("aria-selected", "true");
+    expect(options()[2]).toHaveAttribute("aria-selected", "true");
+  });
+
+  it("handles modifier clicks and resets on filter text changes", async () => {
+    const input = await showFiles();
+    const click = (i: number, modifiers: object) => {
+      fireEvent.mouseDown(options()[i]!, modifiers);
+      fireEvent.click(options()[i]!, modifiers);
+    };
+    click(2, { shiftKey: true });
+    expect(options().filter((r) => r.getAttribute("aria-selected") === "true")).toHaveLength(3);
+    click(1, { metaKey: true });
+    expect(options().filter((r) => r.getAttribute("aria-selected") === "true")).toEqual([options()[0], options()[2]]);
+    expect(openLocation).not.toHaveBeenCalled();
+    fireEvent.change(input, { target: { value: "index" } });
+    expect(options().filter((r) => r.getAttribute("aria-selected") === "true")).toHaveLength(1);
+    click(1, {});
+    await tick();
+    expect(openLocation).toHaveBeenCalledExactlyOnceWith("/p/two/index.ts", null, { side: false });
+  });
+});
+
 describe("Find in Files dialog", () => {
   it("streams results and previews the replacement", async () => {
     render(<FindInFilesOverlay />);
diff --git a/src/features/search/common/open.ts b/src/features/search/common/open.ts
index c5f52601f..a11da3857 100644
--- a/src/features/search/common/open.ts
+++ b/src/features/search/common/open.ts
@@ -82,3 +82,17 @@ export function saveJson(key: string, value: unknown) {
     /* storage unavailable */
   }
 }
+
+/** Open persistent tabs in list order, then restore the lead's focus and position. */
+export async function openInListOrder<T>(
+  items: readonly T[],
+  lead: T | undefined,
+  open: (item: T, options: Omit<OpenOptions, "selection">) => Promise<void>,
+  side = false,
+  afterOpen?: () => Promise<void>,
+): Promise<void> {
+  for (const item of items) await open(item, { preview: false, focus: false, side });
+  await afterOpen?.();
+  const target = lead && items.includes(lead) ? lead : items.at(-1);
+  if (target) await open(target, { preview: false, focus: true, side });
+}
diff --git a/src/features/search/everywhere/SearchEverywhere.tsx b/src/features/search/everywhere/SearchEverywhere.tsx
index f5bd6c410..c5c50460f 100644
--- a/src/features/search/everywhere/SearchEverywhere.tsx
+++ b/src/features/search/everywhere/SearchEverywhere.tsx
@@ -18,12 +18,16 @@ import {
   Select,
   Toggle,
   listNavigate,
+  selectRow,
+  selectedRows,
+  rowSelectionMode,
+  type RowSelection,
   type MenuItem,
   T,
 } from "@/ui";
 import { useFileDecoration } from "@/workbench/contributions";
 import { highlightTokens, languageForPath, type CodeToken } from "@/editor/lsp/markdown";
-import { badgeKind, basename, openLocation, relDir } from "../common/open";
+import { badgeKind, basename, openInListOrder, openLocation, relDir } from "../common/open";
 import { parseLocationQuery } from "../common/query";
 import { CodePreview, type PreviewHighlight } from "../find/parts";
 import { SeController, type SeSnapshot } from "./controller";
@@ -81,7 +85,8 @@ export function SearchEverywhereOverlay() {
   return open ? <SearchEverywhereDialog /> : null;
 }
 
-type Selection = { key: string | null; index: number; moved: boolean };
+type Selection = RowSelection & { key: string | null; anchorKey: string | null; moved: boolean };
+const INITIAL_SELECTION: Selection = { key: null, anchorKey: null, lead: -1, anchor: -1, keys: null, moved: false };
 
 function SearchEverywhereDialog() {
   const tx = useTx();
@@ -100,7 +105,7 @@ function SearchEverywhereDialog() {
   const [extra, setExtra] = useState<Partial<Record<SectionId, number>>>({});
   const [snap, setSnap] = useState<SeSnapshot | null>(null);
   const [controller] = useState(() => new SeController(ipcDeps(ctx), setSnap));
-  const [sel, setSel] = useState<Selection>({ key: null, index: -1, moved: false });
+  const [sel, setSel] = useState<Selection>(INITIAL_SELECTION);
   const [menu, setMenu] = useState<{
     anchor: Element;
     items: MenuItem[];
@@ -134,12 +139,19 @@ function SearchEverywhereDialog() {
     return () => clearTimeout(t);
   }, [query, debounced]);
 
+  // Reset selection immediately, including while the new query is debouncing.
+  const [selectionInputs, setSelectionInputs] = useState({ query, tab });
+  if (selectionInputs.query !== query || selectionInputs.tab !== tab) {
+    setSelectionInputs({ query, tab });
+    setSel(INITIAL_SELECTION);
+  }
+
   // New query / scope: forget "Show more" and the user's selection.
   const [prevInputs, setPrevInputs] = useState({ debounced, tab });
   if (prevInputs.debounced !== debounced || prevInputs.tab !== tab) {
     setPrevInputs({ debounced, tab });
     setExtra({});
-    setSel({ key: null, index: -1, moved: false });
+    setSel(INITIAL_SELECTION);
   }
 
   // "/fi" lists scope commands instead of searching.
@@ -177,7 +189,7 @@ function SearchEverywhereDialog() {
     () => listing ?? (snap ? buildRows(snap.sections, { headers: !parsed.text.trim(), mix }) : []),
     [listing, snap, parsed.text, mix],
   );
-  const active = stableIndex(rows, sel.key, sel.index, sel.moved);
+  const active = stableIndex(rows, sel.key, sel.lead, sel.moved);
   const activeRow = active >= 0 ? rows[active] : undefined;
   // Rows still answer an older query (debounce / in-flight search): Enter must wait.
   const settled =
@@ -187,8 +199,20 @@ function SearchEverywhereDialog() {
     snap.tab === tab &&
     topResultSettled(snap.sections, mix);
   const pendingEnter = useRef<{ side: boolean } | null>(null);
+  const opening = useRef(false);
 
-  const select = (index: number) => setSel({ key: rows[index]?.key ?? null, index, moved: true });
+  const chosen = selectedRows(rows, { ...sel, lead: active });
+  const select = (index: number, e?: KeyboardEvent | MouseEvent) => {
+    const anchor = rows.findIndex((r) => r.key === sel.anchorKey);
+    const next = selectRow(
+      rows,
+      { ...sel, lead: active, anchor: anchor < 0 ? active : anchor },
+      index,
+      rowSelectionMode(e),
+      isSectionRow,
+    );
+    setSel({ ...next, key: rows[next.lead]?.key ?? null, anchorKey: rows[next.anchor]?.key ?? null, moved: true });
+  };
   /** Typed or picked query; "/files foo" switches to Files with "foo". */
   const setQuery = (value: string) => {
     history.current.pos = -1;
@@ -246,24 +270,13 @@ function SearchEverywhereDialog() {
       case "more": {
         const step = tab === "all" ? MORE_STEP_ALL : MORE_STEP_TAB;
         setExtra((e) => ({ ...e, [row.section]: (e[row.section] ?? 0) + step }));
-        setSel({ key: null, index: rows.indexOf(row), moved: true });
+        setSel({ ...INITIAL_SELECTION, lead: rows.indexOf(row), moved: true });
         return;
       }
       case "file":
-        return closeThen(
-          () => void openLocation(row.path, row.line !== null ? { line: row.line, col: row.col ?? 0 } : null, { side }),
-        );
       case "symbol":
-        return closeThen(() => void openLocation(row.path, { line: row.line, col: row.col }, { side }));
       case "text":
-        return closeThen(
-          () =>
-            void openLocation(
-              row.path,
-              { line: row.line, col: row.col, endLine: row.line, endCol: row.endCol },
-              { side },
-            ),
-        );
+        return closeThen(() => void openResult(row, { side }));
       case "action":
         if (!row.enabled) return;
         pushRecentAction(row.id);
@@ -277,11 +290,27 @@ function SearchEverywhereDialog() {
     }
   };
 
+  const activateSelection = (side = false) => {
+    if (opening.current) return;
+    if (chosen.length <= 1) return activate(chosen[0], side);
+    const navigable = chosen.filter(isNavigationRow);
+    if (!navigable.length) return close();
+    opening.current = true;
+    pushSearchHistory(tab, query);
+    void openInListOrder(
+      navigable,
+      activeRow && isNavigationRow(activeRow) ? activeRow : undefined,
+      openResult,
+      side,
+      () => new Promise((resolve) => closeThen(resolve)),
+    );
+  };
+
   useEffect(() => {
     const pending = pendingEnter.current;
     if (!pending || !settled) return;
     pendingEnter.current = null;
-    activate(activeRow, pending.side);
+    activateSelection(pending.side);
   });
 
   /** IDEA's ⌥↵ on an action: record a shortcut for it (written to the active keymap). */
@@ -291,7 +320,7 @@ function SearchEverywhereDialog() {
     const row = activeRow;
     if (!row || row.kind === "section" || row.kind === "more" || row.kind === "command") return;
     if (row.kind === "action") return assignShortcut(row.id);
-    const anchor = listRef.current?.querySelector('[aria-selected="true"]') ?? inputRef.current;
+    const anchor = listRef.current?.querySelector('[data-lead="true"]') ?? inputRef.current;
     if (!anchor) return;
     const copy = (text: string) => void navigator.clipboard?.writeText(text).catch(() => {});
     const items: MenuItem[] =
@@ -331,7 +360,7 @@ function SearchEverywhereDialog() {
         closeThen(() => void executeAction("find.inPath", { query: parsed.text }));
       else if (listing) activate(activeRow);
       else if (!settled && !sel.moved) pendingEnter.current = { side: e.shiftKey };
-      else activate(activeRow, e.shiftKey);
+      else activateSelection(e.shiftKey);
       return;
     }
     if (e.altKey && (e.key === "ArrowUp" || e.key === "ArrowDown")) {
@@ -347,15 +376,15 @@ function SearchEverywhereDialog() {
       const jump = groupJump(rows, active, e.key === "PageDown" || e.key === "ArrowDown" ? 1 : -1);
       if (jump !== null) {
         e.preventDefault();
-        select(jump);
+        select(jump, e);
         return;
       }
     }
     if (!["ArrowDown", "ArrowUp", "PageDown", "PageUp"].includes(e.key)) return;
-    const next = listNavigate(e.key, { items: rows, active, isSection: isSectionRow, wrap: true, pageSize: 10 });
+    const next = listNavigate(e.key, { items: rows, active, isSection: isSectionRow, wrap: !e.shiftKey, pageSize: 10 });
     if (next === null) return;
     e.preventDefault();
-    select(next);
+    select(next, e);
   };
 
   const maxList = preview ? MAX_LIST_PREVIEW : MAX_LIST;
@@ -522,7 +551,8 @@ function SearchEverywhereDialog() {
                 <span className={styles.section}>{r.kind === "section" ? <T>{r.title}</T> : ""}</span>
               )}
               activeIndex={active}
-              onActiveChange={select}
+              onSelect={select}
+              isSelected={(r) => !!sel.keys?.has(r.key)}
               onActivate={(r, _i, e) => activate(r, (e as MouseEvent).shiftKey)}
               focusable={false}
               rowHeight={ROW}
@@ -844,3 +874,21 @@ function FileRow({
     </>
   );
 }
+
+type NavigationRow = Extract<SeRow, { kind: "file" | "symbol" | "text" }>;
+function isNavigationRow(row: SeRow): row is NavigationRow {
+  return row.kind === "file" || row.kind === "symbol" || row.kind === "text";
+}
+function openResult(row: NavigationRow, options: Parameters<typeof openLocation>[2]): Promise<void> {
+  if (row.kind === "file")
+    return openLocation(row.path, row.line !== null ? { line: row.line, col: row.col ?? 0 } : null, options);
+  return openLocation(
+    row.path,
+    {
+      line: row.line,
+      col: row.col,
+      ...(row.kind === "text" ? { endLine: row.line, endCol: row.endCol } : {}),
+    },
+    options,
+  );
+}
diff --git a/src/features/search/find/rowSelection.ts b/src/features/search/find/rowSelection.ts
index 19d35b58a..6930c0073 100644
--- a/src/features/search/find/rowSelection.ts
+++ b/src/features/search/find/rowSelection.ts
@@ -1,52 +1 @@
-/**
- * Multi-selection of the Find in Files results list: click / ↑↓ select one row,
- * ⇧ extends from the anchor, ⌘/Ctrl toggles a row (IDEA's results table).
- */
-
-export interface RowSelection {
-  /** Active row (keyboard focus, preview). */
-  lead: number;
-  /** Start of ⇧ ranges. */
-  anchor: number;
-  /** Keys of the selected rows; `null` when only the lead is selected. */
-  keys: ReadonlySet<string> | null;
-}
-
-export const SINGLE_FIRST: RowSelection = { lead: 0, anchor: 0, keys: null };
-
-export function selectRow(
-  rows: ReadonlyArray<{ key: string }>,
-  sel: RowSelection,
-  index: number,
-  mode: "single" | "range" | "toggle" = "single",
-): RowSelection {
-  if (index < 0 || index >= rows.length) return sel;
-  if (mode === "range") {
-    const anchor = Math.min(Math.max(0, sel.anchor), rows.length - 1);
-    const [a, b] = anchor <= index ? [anchor, index] : [index, anchor];
-    return { lead: index, anchor, keys: new Set(rows.slice(a, b + 1).map((r) => r.key)) };
-  }
-  if (mode === "toggle") {
-    const keys = new Set(sel.keys ?? (rows[sel.lead] ? [rows[sel.lead]!.key] : []));
-    const key = rows[index]!.key;
-    if (!keys.has(key)) return { lead: index, anchor: index, keys: keys.add(key) };
-    keys.delete(key);
-    const rest = rows.findLastIndex((r) => keys.has(r.key));
-    if (rest < 0) return { lead: index, anchor: index, keys: null };
-    return { lead: rest, anchor: rest, keys };
-  }
-  return { lead: index, anchor: index, keys: null };
-}
-
-/** The selected rows in list order (the lead when nothing else is selected). */
-export function selectedRows<T extends { key: string }>(rows: readonly T[], sel: RowSelection): T[] {
-  if (!rows.length) return [];
-  const lead = Math.min(sel.lead, rows.length - 1);
-  if (!sel.keys) return [rows[lead]!];
-  const out = rows.filter((r) => sel.keys!.has(r.key));
-  return out.length ? out : [rows[lead]!];
-}
-
-export function isRowSelected(sel: RowSelection, key: string): boolean {
-  return !!sel.keys?.has(key);
-}
+export { SINGLE_FIRST, isRowSelected, selectRow, selectedRows, type RowSelection } from "@/ui/rowSelection";
diff --git a/src/features/search/recent/RecentPopups.tsx b/src/features/search/recent/RecentPopups.tsx
index efab57b66..a6b79e08b 100644
--- a/src/features/search/recent/RecentPopups.tsx
+++ b/src/features/search/recent/RecentPopups.tsx
@@ -5,7 +5,21 @@ import { editorsFor, getNavigationHistory } from "@/editor/api";
 import { call, commands, type OutlineItem } from "@/platform/ipc";
 import { shortcutLabel } from "@/platform/keymap";
 import { useProject } from "@/platform/project";
-import { Checkbox, Dialog, HighlightedText, Icon, List, fileIconName, listNavigate, T } from "@/ui";
+import {
+  Checkbox,
+  Dialog,
+  HighlightedText,
+  Icon,
+  List,
+  fileIconName,
+  listNavigate,
+  selectRow,
+  selectedRows,
+  rowSelectionMode,
+  SINGLE_FIRST,
+  type RowSelection,
+  T,
+} from "@/ui";
 import {
   maybeEditorService,
   toolWindowService,
@@ -15,7 +29,7 @@ import {
   type ToolWindowContribution,
 } from "@/workbench/contributions";
 import { highlightTokens, languageForPath, type CodeToken } from "@/editor/lsp/markdown";
-import { basename, openLocation } from "../common/open";
+import { basename, openInListOrder, openLocation } from "../common/open";
 import { outlinePathAt } from "../structure/outline";
 import { fromNavigationHistory, isDismissed, mergeLocations, type RecentLocation } from "../common/locations";
 import { dismissLocation, useTracking } from "../common/tracking";
@@ -73,6 +87,14 @@ function RecentFilesDialog() {
   const [column, setColumn] = useState<"files" | "tools">("files");
   const [fileIndex, setFileIndex] = useState<number | null>(null);
   const [toolIndex, setToolIndex] = useState(0);
+  const opening = useRef(false);
+  const [previousEditedOnly, setPreviousEditedOnly] = useState(editedOnly);
+  const [fileSelection, setFileSelection] = useState<RowSelection>(SINGLE_FIRST);
+  if (previousEditedOnly !== editedOnly) {
+    setPreviousEditedOnly(editedOnly);
+    setFileSelection(SINGLE_FIRST);
+    setFileIndex(null);
+  }
   const inputRef = useRef<HTMLInputElement>(null);
   // The current editor: a file path, or the key of a non-file editor (Switcher lists those too).
   const activePath = useMemo(() => {
@@ -106,6 +128,7 @@ function RecentFilesDialog() {
           ),
     [paths, tabs, removed, query, root, edited, editedOnly],
   );
+  const fileRows = useMemo(() => files.map((f) => ({ ...f, key: f.path })), [files]);
   const tools = useMemo(() => switcherToolWindows(toolWindows.values(), !!root, query), [toolWindows, root, query]);
   const fIndex = files.length
     ? Math.min(fileIndex ?? initialFileIndex(files, activePath, query), files.length - 1)
@@ -123,6 +146,31 @@ function RecentFilesDialog() {
     );
   };
 
+  const selectFile = (index: number, e?: KeyboardEvent | ReactMouseEvent) => {
+    const next = selectRow(
+      fileRows,
+      { ...fileSelection, lead: fIndex, anchor: fileSelection.keys ? fileSelection.anchor : fIndex },
+      index,
+      switcher ? "single" : rowSelectionMode(e),
+    );
+    setFileSelection(next);
+    setFileIndex(next.lead);
+    setColumn("files");
+  };
+  const openFiles = (side = false) => {
+    if (opening.current) return;
+    const chosen = selectedRows(fileRows, { ...fileSelection, lead: fIndex });
+    if (chosen.length <= 1) return openFile(chosen[0], side);
+    opening.current = true;
+    void openInListOrder(
+      chosen,
+      fileRows[fIndex],
+      (f, options) => openLocation(f.path, null, options),
+      side,
+      () => new Promise((resolve) => afterClose(resolve)),
+    );
+  };
+
   const openTool = (tw: ToolWindowContribution | undefined) => {
     if (tw) afterClose(() => toolWindowService().show(tw.id, true));
   };
@@ -143,6 +191,7 @@ function RecentFilesDialog() {
     if (!switcher) void call(commands.removeRecent(item.path)).catch(() => {});
     setRemoved((r) => new Set(r).add(item.path));
     setFileIndex(fIndex);
+    setFileSelection({ lead: fIndex, anchor: fIndex, keys: null });
   };
 
   // Switcher: each ⌃⇥ moves one row, past the end into the other column; releasing Ctrl opens the selection.
@@ -182,7 +231,7 @@ function RecentFilesDialog() {
         // Nothing recent matches: carry the text over to Go to File.
         const text = query.trim();
         afterClose(() => showSearchEverywhere("files", { query: text }));
-      } else if (effectiveColumn === "files") openFile(files[fIndex], e.shiftKey);
+      } else if (effectiveColumn === "files") openFiles(e.shiftKey);
       else openTool(tools[tIndex]?.tw);
       return;
     }
@@ -201,6 +250,7 @@ function RecentFilesDialog() {
     if (e.key === "Tab" || ((e.key === "ArrowLeft" || e.key === "ArrowRight") && !query)) {
       e.preventDefault();
       e.stopPropagation();
+      setFileSelection(SINGLE_FIRST);
       setColumn(
         e.key === "ArrowLeft"
           ? "tools"
@@ -215,8 +265,8 @@ function RecentFilesDialog() {
     if (!NAV_KEYS.includes(e.key)) return;
     e.preventDefault();
     if (effectiveColumn === "files") {
-      const next = listNavigate(e.key, { items: files, active: fIndex, wrap: true });
-      if (next !== null) setFileIndex(next);
+      const next = listNavigate(e.key, { items: files, active: fIndex, wrap: switcher || !e.shiftKey });
+      if (next !== null) selectFile(next, e);
     } else {
       const next = listNavigate(e.key, { items: tools, active: tIndex, wrap: true });
       if (next !== null) setToolIndex(next);
@@ -248,6 +298,7 @@ function RecentFilesDialog() {
                 onChange={(e) => {
                   setQuery(e.target.value);
                   setFileIndex(null);
+                  setFileSelection(SINGLE_FIRST);
                   setToolIndex(0);
                 }}
                 onKeyDown={onKeyDown}
@@ -280,6 +331,7 @@ function RecentFilesDialog() {
             getKey={(t) => t.tw.id}
             activeIndex={effectiveColumn === "tools" ? tIndex : -1}
             onActiveChange={(i) => {
+              setFileSelection(SINGLE_FIRST);
               setToolIndex(i);
               setColumn("tools");
             }}
@@ -307,10 +359,9 @@ function RecentFilesDialog() {
             items={files}
             getKey={(f) => f.path}
             activeIndex={effectiveColumn === "files" ? fIndex : -1}
-            onActiveChange={(i) => {
-              setFileIndex(i);
-              setColumn("files");
-            }}
+            onActiveChange={switcher ? (i) => selectFile(i) : undefined}
+            onSelect={switcher ? undefined : selectFile}
+            isSelected={(f) => effectiveColumn === "files" && !!fileSelection.keys?.has(f.path)}
             onActivate={(f, _i, e) => openFile(f, e.shiftKey)}
             focusable={false}
             rowHeight={24}
diff --git a/src/features/settings/__tests__/behavior.test.ts b/src/features/settings/__tests__/behavior.test.ts
index de00873e7..e17a9eb13 100644
--- a/src/features/settings/__tests__/behavior.test.ts
+++ b/src/features/settings/__tests__/behavior.test.ts
@@ -1,7 +1,8 @@
 import { describe, expect, it } from "vitest";
 import { formatPattern, formatTimestamp } from "@/platform/dateFormat";
 import { resolveThemeId } from "@/workbench/theme";
-import { nextZoom } from "../appearanceRuntime";
+import { applyAppearanceOptions, nextZoom } from "../appearanceRuntime";
+import { validateSettings } from "../model/schema";
 import { validateAppearanceExtras, validateNotifications } from "../model/behaviorSchema";
 
 describe("appearance & behavior settings", () => {
@@ -21,6 +22,33 @@ describe("appearance & behavior settings", () => {
     expect(validateAppearanceExtras({ theme: "system" }).syncWithOs).toBe(true);
   });
 
+  it("defaults Show tool window badges to on and honours the stored value", () => {
+    expect(validateAppearanceExtras({}).showToolWindowBadges).toBe(true);
+    expect(validateAppearanceExtras({ showToolWindowBadges: false }).showToolWindowBadges).toBe(false);
+    expect(validateAppearanceExtras({ showToolWindowBadges: 1 }).showToolWindowBadges).toBe(true);
+  });
+
+  it("keeps the UI fallback font empty by default and trims a stored one", () => {
+    expect(validateAppearanceExtras({}).uiFontFallback).toBe("");
+    expect(validateAppearanceExtras({ uiFontFallback: " 思源黑体 " }).uiFontFallback).toBe("思源黑体");
+    expect(validateAppearanceExtras({ uiFontFallback: 5 }).uiFontFallback).toBe("");
+  });
+
+  it("applies and clears the UI fallback, and removes custom fonts when disabled", () => {
+    const root = document.createElement("div");
+    const settings = validateSettings({
+      appearance: { useCustomFont: true, uiFontFamily: "Menlo", uiFontFallback: "Songti SC" },
+    });
+    applyAppearanceOptions(settings, root);
+    expect(root.style.getPropertyValue("--font-ui")).toBe('"Menlo", "Songti SC", system-ui, sans-serif');
+    settings.appearance.uiFontFallback = "";
+    applyAppearanceOptions(settings, root);
+    expect(root.style.getPropertyValue("--font-ui")).toBe('"Menlo", system-ui, sans-serif');
+    settings.appearance.useCustomFont = false;
+    applyAppearanceOptions(settings, root);
+    expect(root.style.getPropertyValue("--font-ui")).toBe("");
+  });
+
   it("formats dates with an override pattern and pretty dates", () => {
     const d = new Date(2026, 0, 5, 14, 7);
     expect(formatPattern(d, "dd.MM.yyyy")).toBe("05.01.2026");
diff --git a/src/features/settings/__tests__/dialog.test.tsx b/src/features/settings/__tests__/dialog.test.tsx
index 4a11b98c0..dbdb5f024 100644
--- a/src/features/settings/__tests__/dialog.test.tsx
+++ b/src/features/settings/__tests__/dialog.test.tsx
@@ -222,6 +222,24 @@ describe("Settings dialog", () => {
     ]);
   });
 
+  it("enables, saves and clears the custom UI fallback font", async () => {
+    const dialog = await openDialog("appearance");
+    const fallback = within(dialog).getByRole("combobox", { name: "UI fallback font" });
+    const custom = within(dialog).getByRole("checkbox", { name: "Use custom font:" });
+    expect(fallback).toBeDisabled();
+    fireEvent.click(custom);
+    expect(fallback).toBeEnabled();
+    fireEvent.change(fallback, { target: { value: "Songti SC" } });
+    expect(settingsSet).not.toHaveBeenCalled();
+    await act(async () => fireEvent.click(within(dialog).getByRole("button", { name: "Apply" })));
+    expect(settingsSet).toHaveBeenCalledWith("global", "appearance.uiFontFallback", JSON.stringify("Songti SC"));
+    fireEvent.change(fallback, { target: { value: "" } });
+    await act(async () => fireEvent.click(within(dialog).getByRole("button", { name: "Apply" })));
+    expect(settingsSet).toHaveBeenCalledWith("global", "appearance.uiFontFallback", JSON.stringify(""));
+    fireEvent.click(custom);
+    expect(fallback).toBeDisabled();
+  });
+
   it("edits and saves independent custom font weights", async () => {
     const dialog = await openDialog("editor.font");
     for (const [label, value] of [
diff --git a/src/features/settings/__tests__/languages.test.ts b/src/features/settings/__tests__/languages.test.ts
index 0fd9ac555..5864b0586 100644
--- a/src/features/settings/__tests__/languages.test.ts
+++ b/src/features/settings/__tests__/languages.test.ts
@@ -35,6 +35,16 @@ describe("languages settings", () => {
     expect(validateSettings({}).languages).toEqual(DEFAULT_LANGUAGES);
   });
 
+  it("keeps Prettier opt-in on save and normalizes its enabled languages", () => {
+    expect(validateLanguages({}).prettier).toMatchObject({ prefer: false, runOnSave: false, path: "" });
+    expect(
+      validateLanguages({
+        prettier: { path: " ./bin/prettier ", languages: ["markdown", 4, "markdown"], prefer: true, runOnSave: true },
+      }).prettier,
+    ).toEqual({ path: "./bin/prettier", languages: ["markdown"], prefer: true, runOnSave: true });
+    expect(validateLanguages({ prettier: { languages: [] } }).prettier.languages).toEqual([]);
+  });
+
   it("marks folders with one role each", () => {
     expect(normalizeFolder("./src/main/")).toBe("src/main");
     let ps = validateProjectStructure({ sourceRoots: ["src/", "src", 3], excluded: ["/dist"] });
@@ -58,6 +68,7 @@ describe("language pages", () => {
       "Java",
       "Node.js",
       "Python Interpreter",
+      "Prettier",
       "Rust",
       "TypeScript",
     ]);
diff --git a/src/features/settings/appearanceRuntime.ts b/src/features/settings/appearanceRuntime.ts
index 3052bf659..c60c5744b 100644
--- a/src/features/settings/appearanceRuntime.ts
+++ b/src/features/settings/appearanceRuntime.ts
@@ -33,7 +33,7 @@ export function applyAppearanceOptions(s: ValidSettings, root: HTMLElement = doc
     if (size === DEFAULT_SETTINGS.appearance.uiFontSize) root.style.removeProperty(name);
     else root.style.setProperty(name, `${size + delta}px`);
   }
-  if (a.useCustomFont) root.style.setProperty("--font-ui", uiFontFamily(a.uiFontFamily));
+  if (a.useCustomFont) root.style.setProperty("--font-ui", uiFontFamily(a.uiFontFamily, a.uiFontFallback));
   else root.style.removeProperty("--font-ui");
 
   flag(root, "compact", a.compactMode);
diff --git a/src/features/settings/languages/PrettierPage.tsx b/src/features/settings/languages/PrettierPage.tsx
new file mode 100644
index 000000000..ea20c7b01
--- /dev/null
+++ b/src/features/settings/languages/PrettierPage.tsx
@@ -0,0 +1,72 @@
+import { useId } from "react";
+import { Input } from "@/ui";
+import { Row, Section, Select, Toggle } from "../components/Form";
+import { useSetting } from "../components/context";
+import { DEFAULT_LANGUAGES } from "@/platform/languageSettings";
+
+const names: Record<string, string> = {
+  markdown: "Markdown",
+  yaml: "YAML",
+  css: "CSS",
+  scss: "SCSS",
+  less: "Less",
+  html: "HTML",
+  graphql: "GraphQL",
+  javascript: "JavaScript",
+  javascriptreact: "JavaScript JSX",
+  typescript: "TypeScript",
+  typescriptreact: "TypeScript JSX",
+  json: "JSON",
+  jsonc: "JSON with Comments",
+  vue: "Vue",
+};
+
+export function PrettierPage() {
+  const id = useId();
+  const [path, setPath] = useSetting<string>("languages.prettier.path");
+  const [languages, setLanguages] = useSetting<string[]>("languages.prettier.languages");
+  const [prefer, setPrefer] = useSetting<boolean>("languages.prettier.prefer");
+  const [save, setSave] = useSetting<boolean>("languages.prettier.runOnSave");
+  return (
+    <>
+      <Section title="Prettier">
+        <Row
+          label="Prettier path"
+          htmlFor={id}
+          hint="Auto: nearest project node_modules, managed installation, then PATH. An explicit path overrides auto detection."
+        >
+          <Input id={id} mono value={path} placeholder="Auto" onChange={(e) => setPath(e.target.value)} />
+        </Row>
+        <Row label="Formatting provider">
+          <Select
+            value={prefer ? "prettier" : "auto"}
+            onChange={(v) => setPrefer(v === "prettier")}
+            aria-label="Formatting provider"
+            options={[
+              { value: "auto", label: "Automatic (language server first)" },
+              { value: "prettier", label: "Prettier" },
+            ]}
+          />
+        </Row>
+        <Toggle
+          label="Run on save"
+          checked={save}
+          onChange={setSave}
+          hint="Run Prettier on save for enabled languages when it is the selected formatting provider."
+        />
+      </Section>
+      <Section title="Enabled languages">
+        {DEFAULT_LANGUAGES.prettier.languages.map((language) => (
+          <Toggle
+            key={language}
+            label={names[language]!}
+            checked={languages.includes(language)}
+            onChange={(checked) =>
+              setLanguages(checked ? [...languages, language] : languages.filter((l) => l !== language))
+            }
+          />
+        ))}
+      </Section>
+    </>
+  );
+}
diff --git a/src/features/settings/model/behaviorSchema.ts b/src/features/settings/model/behaviorSchema.ts
index 6ee7b326f..d1dacd1ee 100644
--- a/src/features/settings/model/behaviorSchema.ts
+++ b/src/features/settings/model/behaviorSchema.ts
@@ -20,6 +20,7 @@ export interface AppearanceExtras {
   zoom: number;
   useCustomFont: boolean;
   uiFontFamily: string;
+  uiFontFallback: string;
   contrastScrollbars: boolean;
   redGreenVision: boolean;
   differentToolWindowBackground: boolean;
@@ -33,6 +34,7 @@ export interface AppearanceExtras {
   editorAntialiasing: Antialiasing;
   showToolWindowBars: boolean;
   showToolWindowNames: boolean;
+  showToolWindowBadges: boolean;
   widescreenToolWindows: boolean;
 }
 
@@ -71,6 +73,7 @@ export const DEFAULT_APPEARANCE_EXTRAS: AppearanceExtras = {
   zoom: 100,
   useCustomFont: false,
   uiFontFamily: "Inter",
+  uiFontFallback: "",
   contrastScrollbars: false,
   redGreenVision: false,
   differentToolWindowBackground: false,
@@ -84,6 +87,7 @@ export const DEFAULT_APPEARANCE_EXTRAS: AppearanceExtras = {
   editorAntialiasing: "greyscale",
   showToolWindowBars: true,
   showToolWindowNames: false,
+  showToolWindowBadges: true,
   widescreenToolWindows: false,
 };
 
@@ -121,6 +125,7 @@ export function validateAppearanceExtras(raw: unknown): AppearanceExtras {
     zoom: int(a.zoom, d.zoom, ZOOM_LIMITS),
     useCustomFont: b("useCustomFont"),
     uiFontFamily: typeof a.uiFontFamily === "string" && a.uiFontFamily.trim() ? a.uiFontFamily.trim() : d.uiFontFamily,
+    uiFontFallback: typeof a.uiFontFallback === "string" ? a.uiFontFallback.trim() : d.uiFontFallback,
     contrastScrollbars: b("contrastScrollbars"),
     redGreenVision: b("redGreenVision"),
     differentToolWindowBackground: b("differentToolWindowBackground"),
@@ -134,6 +139,7 @@ export function validateAppearanceExtras(raw: unknown): AppearanceExtras {
     editorAntialiasing: oneOf(a.editorAntialiasing, AA, d.editorAntialiasing),
     showToolWindowBars: b("showToolWindowBars"),
     showToolWindowNames: b("showToolWindowNames"),
+    showToolWindowBadges: b("showToolWindowBadges"),
     widescreenToolWindows: b("widescreenToolWindows"),
   };
 }
diff --git a/src/features/settings/pages/Behavior.module.css b/src/features/settings/pages/Behavior.module.css
index a1c511bbc..0a36ad272 100644
--- a/src/features/settings/pages/Behavior.module.css
+++ b/src/features/settings/pages/Behavior.module.css
@@ -24,7 +24,7 @@
   padding: 8px 14px;
 }
 
-/* "[x] Use custom font: [Inter] Size: [13]" */
+/* Inline option groups, with custom font controls wrapping together. */
 .fontRow {
   display: flex;
   align-items: center;
@@ -37,8 +37,17 @@
 .fontInput {
   width: 220px;
 }
-.sizeLabel {
-  margin-left: 8px;
+.customFontRow {
+  flex-wrap: wrap;
+}
+.fontOption {
+  display: inline-flex;
+  align-items: center;
+  gap: 8px;
+  max-width: 100%;
+}
+.fontOption > label {
+  flex-shrink: 0;
 }
 .sizeInput {
   width: 64px;
diff --git a/src/features/settings/pages/behavior.tsx b/src/features/settings/pages/behavior.tsx
index ed4f12ae9..6143d3abb 100644
--- a/src/features/settings/pages/behavior.tsx
+++ b/src/features/settings/pages/behavior.tsx
@@ -181,35 +181,53 @@ function ZoomRow() {
 function CustomFontRow() {
   const [on, setOn] = useSetting<boolean>("appearance.useCustomFont");
   const [family, setFamily] = useSetting<string>("appearance.uiFontFamily");
+  const [fallback, setFallback] = useSetting<string>("appearance.uiFontFallback");
   const [size, setSize] = useSetting<number>("appearance.uiFontSize");
   const id = useId();
   const matched = useLabelMatch("Use custom font");
   return (
-    <div className={clsx(styles.fontRow, matched && styles.matched)}>
-      <Checkbox checked={on} onChange={setOn} label={<SearchLabel text="Use custom font:" />} />
-      <FontPicker label="UI font" disabled={!on} value={family} onChange={setFamily} />
-      <label className={clsx(styles.sizeLabel, !on && styles.disabled)} htmlFor={`${id}-size`}>
-        <SearchLabel text="Size:" />
-      </label>
-      {on ? (
-        <NumberInput
-          id={`${id}-size`}
-          value={size}
-          onChange={setSize}
-          {...LIMITS.uiFontSize}
-          integer
-          aria-label="UI font size"
+    <div className={clsx(styles.fontRow, styles.customFontRow, matched && styles.matched)}>
+      <span className={styles.fontOption}>
+        <Checkbox checked={on} onChange={setOn} label={<SearchLabel text="Use custom font:" />} />
+        <FontPicker label="UI font" disabled={!on} value={family} onChange={setFamily} />
+      </span>
+      <span className={styles.fontOption}>
+        <label className={clsx(!on && styles.disabled)} htmlFor={`${id}-fallback`}>
+          <SearchLabel text="Fallback font:" />
+        </label>
+        <FontPicker
+          id={`${id}-fallback`}
+          label="UI fallback font"
+          disabled={!on}
+          value={fallback}
+          onChange={setFallback}
+          allowEmpty
         />
-      ) : (
-        <Input
-          id={`${id}-size`}
-          className={styles.sizeInput}
-          value={String(size)}
-          disabled
-          aria-label="UI font size"
-          readOnly
-        />
-      )}
+      </span>
+      <span className={styles.fontOption}>
+        <label className={clsx(!on && styles.disabled)} htmlFor={`${id}-size`}>
+          <SearchLabel text="Size:" />
+        </label>
+        {on ? (
+          <NumberInput
+            id={`${id}-size`}
+            value={size}
+            onChange={setSize}
+            {...LIMITS.uiFontSize}
+            integer
+            aria-label="UI font size"
+          />
+        ) : (
+          <Input
+            id={`${id}-size`}
+            className={styles.sizeInput}
+            value={String(size)}
+            disabled
+            aria-label="UI font size"
+            readOnly
+          />
+        )}
+      </span>
     </div>
   );
 }
@@ -284,6 +302,11 @@ function ToolWindowsGrid() {
         <>
           <BoundToggle k="appearance.showToolWindowBars" label="Show tool window bars" />
           <BoundToggle k="appearance.showToolWindowNames" label="Show tool window names" />
+          <BoundToggle
+            k="appearance.showToolWindowBadges"
+            label="Show tool window badges"
+            hint="Counts on the stripe icons, e.g. changed files or agent tasks needing input"
+          />
         </>
       }
       right={
@@ -526,7 +549,7 @@ export const BEHAVIOR_PAGES: PageSpec[] = [
           {
             kind: "custom",
             label: "Use custom font",
-            keywords: ["UI font size", "Size", "font family"],
+            keywords: ["UI font size", "Size", "font family", "fallback font"],
             component: CustomFontRow,
           },
           { kind: "toggle", key: "appearance.contrastScrollbars", label: "Use contrast scrollbars" },
diff --git a/src/features/settings/pages/languages.tsx b/src/features/settings/pages/languages.tsx
index b8c320c46..181afc052 100644
--- a/src/features/settings/pages/languages.tsx
+++ b/src/features/settings/pages/languages.tsx
@@ -4,6 +4,7 @@
  * `../languages/`; settings are `languages.*` / `projectStructure.*`.
  */
 import { GoPage, JavaPage, NodePage, RustPage, TypeScriptPage } from "../languages/LanguagePages";
+import { PrettierPage } from "../languages/PrettierPage";
 import { ProjectStructurePage } from "../languages/ProjectStructurePage";
 import { PythonInterpreterPage } from "../languages/PythonInterpreterPage";
 import { GoBuildTagsPage, GO_BUILD_TAG_SECTIONS } from "../languages/GoBuildTags";
@@ -107,6 +108,16 @@ export const LANGUAGE_PAGES: PageSpec[] = [
     keywords: ["node interpreter", "package manager", "npm", "pnpm", "yarn", "bun", "nvm"],
     component: NodePage,
   },
+  {
+    id: "languages.prettier",
+    projectScope: true,
+    defaultScope: "project",
+    title: "Prettier",
+    group: LANGUAGES_GROUP,
+    order: 403.5,
+    keywords: ["formatter", "prettier", "markdown", "yaml", "css", "format on save", "node_modules"],
+    component: PrettierPage,
+  },
   {
     id: "languages.rust",
     projectScope: true,
diff --git a/src/features/terminal/theme.ts b/src/features/terminal/theme.ts
index 5996a12dc..5eeb02b9b 100644
--- a/src/features/terminal/theme.ts
+++ b/src/features/terminal/theme.ts
@@ -6,7 +6,7 @@
  */
 import type { ITheme, Terminal } from "@xterm/xterm";
 import { fontWeightOf } from "@/platform/editorSettings";
-import { BUNDLED_MONO_FAMILY, fontsLoaded, monoFontFamily, monoStack } from "@/platform/fonts";
+import { BUNDLED_MONO_FAMILY, familyFaces, fontsLoaded, monoFontFamily, monoStack } from "@/platform/fonts";
 import { parseColor, type Rgba } from "@/platform/cssColor";
 
 export { parseColor, type Rgba };
@@ -152,9 +152,7 @@ const NERD_FONT_FALLBACKS = [
   "FiraCode Nerd Font",
   "Hasklug Nerd Font",
   "CaskaydiaCove Nerd Font",
-]
-  .map((f) => `"${f}"`)
-  .join(", ");
+];
 
 export interface TerminalFontSettings {
   useEditorFont: boolean;
@@ -189,7 +187,8 @@ export interface TerminalFont {
  * common installs before the generic family so per-glyph fallback finds them.
  */
 function withNerdFonts(family: string): string {
-  return `${family.replace(/,\s*monospace\s*$/i, "")}, ${NERD_FONT_FALLBACKS}, monospace`;
+  const fallbacks = NERD_FONT_FALLBACKS.flatMap(familyFaces).join(", ");
+  return `${family.replace(/,\s*monospace\s*$/i, "")}, ${fallbacks}, monospace`;
 }
 
 function cssNumber(name: string): number {
diff --git a/src/features/tools/LanguageServersPage.tsx b/src/features/tools/LanguageServersPage.tsx
index 933b34cda..206456514 100644
--- a/src/features/tools/LanguageServersPage.tsx
+++ b/src/features/tools/LanguageServersPage.tsx
@@ -39,6 +39,7 @@ const KIND_LABEL: Record<ToolInfo["kind"], string> = {
   languageServer: "Language server",
   debugger: "Debugger",
   plugin: "Plugin",
+  formatter: "Formatter",
 };
 
 export function filterTools(tools: readonly ToolInfo[], query: string, filter: Filter): ToolInfo[] {
diff --git a/src/features/tools/__tests__/tools.test.tsx b/src/features/tools/__tests__/tools.test.tsx
index 4d4c6e9f2..0d4bd57cc 100644
--- a/src/features/tools/__tests__/tools.test.tsx
+++ b/src/features/tools/__tests__/tools.test.tsx
@@ -7,7 +7,7 @@ import { useTasks } from "@/workbench/tasks";
 import { MemoryToolsBackend, sampleTools, setToolsBackend } from "../backend";
 import { cancelInstall, installTool, refreshTools, uninstallTool, useTools } from "../store";
 import { filterTools, LanguageServersPage } from "../LanguageServersPage";
-import { installMissingServerPrompts, missingKey } from "../missing";
+import { installMissingServerPrompts, missingKey, promptInstall } from "../missing";
 import { resetTestForm, stagedFor, TestSettingsForm } from "./settingsForm";
 
 type Note = Parameters<NotificationService["notify"]>[0];
@@ -104,6 +104,34 @@ describe("tools store", () => {
 });
 
 describe("missing language server prompt", () => {
+  it("uses the same install prompt for Prettier with a Reformat Code explanation", async () => {
+    const template = sampleTools()[0]!;
+    backend.tools.push({
+      ...template,
+      name: "prettier",
+      displayName: "Prettier",
+      command: "prettier",
+      kind: "formatter",
+      status: "missing",
+      installMethod: "npm",
+      languages: ["Markdown"],
+    });
+    await promptInstall("prettier");
+    expect(notes[0]).toMatchObject({
+      title: "Prettier is not installed",
+      key: missingKey("prettier"),
+      sticky: true,
+      body: "Reformat Code needs Prettier. Install it via npm?",
+    });
+    expect(notes[0]!.actions!.map((a) => a.label)).toEqual(["Install", "Language Servers…"]);
+    await promptInstall("prettier", false);
+    expect(notes.at(-1)).toMatchObject({ key: missingKey("prettier"), sticky: false });
+    notes[0]!.actions![0]!.run();
+    await waitFor(() =>
+      expect(notes.at(-1)).toMatchObject({ title: "Prettier installed", key: missingKey("prettier") }),
+    );
+  });
+
   it("offers Install for installable servers, once, replacing the generic notice", async () => {
     const off = installMissingServerPrompts();
     const ev = { type: "languageServer", server: 1, name: "gopls", status: "missing", message: null } as const;
diff --git a/src/features/tools/index.ts b/src/features/tools/index.ts
index 5086f5781..76736a609 100644
--- a/src/features/tools/index.ts
+++ b/src/features/tools/index.ts
@@ -9,7 +9,7 @@ import { lazyComponent } from "@/ui";
 import { executeAction, registerActions } from "@/platform/actions";
 import { registerSettingsPage } from "@/workbench/contributions";
 import { installJdkPrompts, registerJdkActions } from "./jdk";
-import { installMissingServerPrompts } from "./missing";
+import { installMissingServerPrompts, promptInstall } from "./missing";
 import { installTool, refreshTools, SETTINGS_PAGE_ID, toolByName, useTools } from "./store";
 
 /** The Language Servers page (also used by the Settings window). */
@@ -40,6 +40,16 @@ export function activate(): () => void {
   const disposers = [
     activateSettingsPages(),
     registerActions([
+      {
+        id: "tools.promptInstall",
+        title: "Install Missing Tool",
+        hidden: true,
+        run: async ({ arg }) => {
+          if (arg && typeof arg === "object" && "name" in arg && typeof arg.name === "string") {
+            await promptInstall(arg.name, !("sticky" in arg) || arg.sticky !== false);
+          }
+        },
+      },
       {
         id: "tools.languageServers",
         title: "Language Servers…",
diff --git a/src/features/tools/missing.ts b/src/features/tools/missing.ts
index e5af938e9..c1c48d1a2 100644
--- a/src/features/tools/missing.ts
+++ b/src/features/tools/missing.ts
@@ -12,7 +12,7 @@ import { tx } from "@/platform/i18n";
 
 export const missingKey = (name: string) => `lsp-missing-${name}`;
 
-export async function promptInstall(name: string): Promise<boolean> {
+export async function promptInstall(name: string, sticky = true): Promise<boolean> {
   if (!useTools.getState().loaded) await refreshTools();
   const tool = toolByName(name);
   if (!tool || !tool.canInstall || tool.status !== "missing") return false;
@@ -26,16 +26,19 @@ export async function promptInstall(name: string): Promise<boolean> {
         t.status !== "missing" &&
         t.languages.some((l) => tool.languages.includes(l)),
     );
-  if (served) return false;
+  if (tool.kind !== "formatter" && served) return false;
   const key = missingKey(name);
   const langs = tool.languages.length ? tool.languages.join(", ") : "these files";
   notifications().notify({
     group: "tools",
     level: "warning",
-    title: `${tool.displayName} is not installed`,
-    body: tx`Code insight for ${langs} needs ${tool.command}. Install it via ${tool.installMethod}?`,
+    title: tx`${tool.displayName} is not installed`,
+    body:
+      tool.kind === "formatter"
+        ? tx`Reformat Code needs ${tool.displayName}. Install it via ${tool.installMethod}?`
+        : tx`Code insight for ${langs} needs ${tool.command}. Install it via ${tool.installMethod}?`,
     key,
-    sticky: true,
+    sticky,
     actions: [
       { label: "Install", run: () => void installTool(name, { notificationKey: key }) },
       { label: "Language Servers…", run: () => void executeAction("file.settings", SETTINGS_PAGE_ID) },
diff --git a/src/features/vcs/ComparisonTree.tsx b/src/features/vcs/ComparisonTree.tsx
new file mode 100644
index 000000000..e2fd952c6
--- /dev/null
+++ b/src/features/vcs/ComparisonTree.tsx
@@ -0,0 +1,78 @@
+import { useState, type ReactNode } from "react";
+import { Icon, Tree, fileIconName } from "@/ui";
+import { DiffEditor } from "./DiffEditor";
+import { diffInput, openDiff, type DiffData } from "./diffInput";
+import { dirKeys, type FileTreeNode } from "./fileTree";
+import styles from "./common.module.css";
+
+/** Shared changes tree and on-demand diff surface for revisions and disk folders. */
+export function ComparisonTree<F>({
+  tree,
+  current,
+  onSelect,
+  diffFor,
+  renderDetails,
+  ariaLabel,
+  openOnActivate = false,
+  getColor,
+  onOpen,
+}: {
+  tree: FileTreeNode<F>[];
+  current: F | null;
+  onSelect: (entry: F | null) => void;
+  diffFor: (entry: F) => DiffData | null;
+  renderDetails: (node: FileTreeNode<F>) => ReactNode;
+  ariaLabel: string;
+  openOnActivate?: boolean;
+  getColor?: (entry: F) => string | undefined;
+  onOpen?: () => void;
+}) {
+  const [selected, setSelected] = useState<ReadonlySet<string>>(new Set());
+  const [expanded, setExpanded] = useState<ReadonlySet<string> | null>(null);
+  const data = current && diffFor(current);
+  const input = data ? diffInput(data) : null;
+  return (
+    <div className={`${styles.comparison} ${input ? styles.comparisonWithDiff : ""}`}>
+      <Tree<FileTreeNode<F>>
+        roots={tree}
+        getKey={(n) => n.key}
+        getLabel={(n) => n.name}
+        getChildren={(n) => (n.file ? undefined : n.children)}
+        isExpandable={(n) => !n.file}
+        expanded={expanded ?? new Set(dirKeys(tree))}
+        onExpandedChange={setExpanded}
+        selected={selected}
+        onSelectionChange={(sel, lead) => {
+          setSelected(sel);
+          onSelect(lead?.file ?? lead?.directory ?? null);
+        }}
+        onActivate={(n) => {
+          const entry = n.file ?? n.directory;
+          if (!entry) return;
+          onSelect(entry);
+          const diff = diffFor(entry);
+          if (openOnActivate && diff) {
+            void openDiff(diff);
+            onOpen?.();
+          }
+        }}
+        aria-label={ariaLabel}
+        className={styles.comparisonTree}
+        renderNode={(n) => (
+          <span className={styles.fileRow} style={{ flex: 1, padding: 0 }}>
+            <Icon name={n.file ? fileIconName(n.name) : "folder"} size={14} />
+            <span className={styles.fileName} style={{ color: n.file ? getColor?.(n.file) : undefined }}>
+              {n.name}
+            </span>
+            {renderDetails(n)}
+          </span>
+        )}
+      />
+      {input && (
+        <div className={styles.comparisonDiff}>
+          <DiffEditor key={input.key} input={input} />
+        </div>
+      )}
+    </div>
+  );
+}
diff --git a/src/features/vcs/DiffEditor.tsx b/src/features/vcs/DiffEditor.tsx
index 49a2dc674..f44a47d02 100644
--- a/src/features/vcs/DiffEditor.tsx
+++ b/src/features/vcs/DiffEditor.tsx
@@ -200,6 +200,7 @@ export function DiffEditor({ input }: { input: EditorInput }) {
   const data = input.data as DiffData;
   const { path, left, right } = data;
   const [attached, setAttached] = useState<Attached | null>(null);
+  const [binary, setBinary] = useState<boolean | null>(null);
   /** Text of the sides that are not live documents. */
   const [statics, setStatics] = useState<{ a: string | null; b: string | null } | null>(null);
   const [error, setError] = useState<string | null>(null);
@@ -263,15 +264,18 @@ export function DiffEditor({ input }: { input: EditorInput }) {
   const reload = useCallback(async () => {
     if (!attached) return;
     try {
-      const [a, b] = await Promise.all([
+      const paths = [sideFile(left, path), sideFile(right, path)].filter((p): p is string => !!p);
+      const [a, b, probes] = await Promise.all([
         attached.a ? null : loadSide(path, left),
         attached.b ? null : loadSide(path, right),
+        Promise.all(paths.map((p) => call(commands.fsProbe(p)).catch(() => null))),
       ]);
       const prev = staticsRef.current;
       if (!prev || prev.a !== a || prev.b !== b) {
         staticsRef.current = { a, b };
         setStatics({ a, b });
       }
+      setBinary(probes.some((p) => p?.binary));
       setError(null);
     } catch (e) {
       setError(errorMessage(e));
@@ -311,9 +315,9 @@ export function DiffEditor({ input }: { input: EditorInput }) {
     left.rev === "HEAD" &&
     !left.path &&
     isWorktree(right);
-  const editableA = !!attached?.a && !attached.a.readOnly;
-  const editableB = !!attached?.b && !attached.b.readOnly;
-  const ready = !!attached && !!statics && lang !== null;
+  const editableA = !binary && !!attached?.a && !attached.a.readOnly;
+  const editableB = !binary && !!attached?.b && !attached.b.readOnly;
+  const ready = !!attached && !!statics && lang !== null && binary !== null;
 
   // Read when the views are built; toggling it later goes through `setSync`.
   const syncScroll = useRef(opts.syncScroll);
@@ -983,7 +987,8 @@ export function DiffEditor({ input }: { input: EditorInput }) {
         <span className={styles.sep} />
         <IconButton icon="refresh" title="Refresh" size="small" onClick={() => void reload()} />
         <span className={styles.count}>
-          {!ready
+          {binary && tx("Binary content")}
+          {!ready || binary
             ? ""
             : chunkInfo.count === 0
               ? identical
@@ -1047,7 +1052,11 @@ export function DiffEditor({ input }: { input: EditorInput }) {
           />
         </div>
       )}
-      {error ? (
+      {binary ? (
+        <div className={styles.message}>
+          <T>Binary files cannot be shown as text</T>
+        </div>
+      ) : error ? (
         <div className={styles.message}>{error}</div>
       ) : !ready ? (
         <div className={styles.message}>
@@ -1061,7 +1070,7 @@ export function DiffEditor({ input }: { input: EditorInput }) {
           opts.highlight === "none" && styles.noHighlight,
           opts.mode === "split" && (opts.alignChanges ? !opts.syncScroll && styles.unsynced : styles.unaligned),
         )}
-        hidden={!!error || !ready}
+        hidden={!!binary || !!error || !ready}
         aria-label={diffTitle(data)}
         role="region"
         onContextMenu={onContextMenu}
diff --git a/src/features/vcs/DirectoryCompare.tsx b/src/features/vcs/DirectoryCompare.tsx
new file mode 100644
index 000000000..b70e2acad
--- /dev/null
+++ b/src/features/vcs/DirectoryCompare.tsx
@@ -0,0 +1,291 @@
+import { useEffect, useMemo, useRef, useState } from "react";
+import { Channel } from "@tauri-apps/api/core";
+import type { DirectoryCompareEntry, DirectoryCompareProgress, DirectoryCompareStatus } from "@/bindings";
+import { call, commands, emitLocalIdeEvent, IpcError, isCancelled, nextRequestId } from "@/platform/ipc";
+import { notifyFileOperation } from "@/platform/fileOps";
+import { tx } from "@/platform/i18n";
+import { Button, Checkbox, Dialog, Input, Spinner, T } from "@/ui";
+import { upsertTask } from "@/workbench/tasks";
+import { ComparisonTree } from "./ComparisonTree";
+import { buildFileTree } from "./fileTree";
+import { confirmDialog, openDialog } from "./dialogs";
+import { openDiff, type DiffData, type DiffSide } from "./diffInput";
+import { compareFilesData } from "./compareData";
+import styles from "./common.module.css";
+
+const STATUS: Record<DirectoryCompareStatus, string> = {
+  leftOnly: "Only on left",
+  rightOnly: "Only on right",
+  different: "Contents differ",
+  equal: "Identical",
+};
+const join = (root: string, path: string) => `${root.replace(/\/$/, "")}/${path}`;
+const directory = (e: DirectoryCompareEntry) => e.leftKind === "dir" || e.rightKind === "dir";
+
+export function directoryDiff(left: string, right: string, entry: DirectoryCompareEntry): DiffData | null {
+  if (directory(entry)) return null;
+  const data = compareFilesData(join(left, entry.path), join(right, entry.path));
+  const missing = (): DiffSide => ({ type: "text", text: "", label: tx("(does not exist)") });
+  return {
+    ...data,
+    title: entry.path,
+    left:
+      entry.leftKind === "symlink"
+        ? { type: "text", text: entry.leftLink ?? "", label: data.left.label ?? join(left, entry.path) }
+        : entry.leftKind
+          ? data.left
+          : missing(),
+    right:
+      entry.rightKind === "symlink"
+        ? { type: "text", text: entry.rightLink ?? "", label: data.right.label ?? join(right, entry.path) }
+        : entry.rightKind
+          ? data.right
+          : missing(),
+  };
+}
+
+export function showDirectoryComparison(left: string, right: string) {
+  if (left === right) return;
+  openDialog((close) => <DirectoryCompareDialog left={left} right={right} onClose={close} />);
+}
+
+export function DirectoryCompareDialog({ left, right, onClose }: { left: string; right: string; onClose: () => void }) {
+  const [entries, setEntries] = useState<DirectoryCompareEntry[]>([]);
+  const [current, setCurrent] = useState<DirectoryCompareEntry | null>(null);
+  const [showEqual, setShowEqual] = useState(false);
+  const [filter, setFilter] = useState("");
+  const [generation, setGeneration] = useState(0);
+  const [busy, setBusy] = useState(true);
+  const [operating, setOperating] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+  const [operationError, setOperationError] = useState<string | null>(null);
+  const [progress, setProgress] = useState<DirectoryCompareProgress | null>(null);
+  const [cancelled, setCancelled] = useState(false);
+  const cancel = useRef<() => void>(() => {});
+  const mounted = useRef(true);
+  useEffect(() => {
+    mounted.current = true;
+    return () => {
+      mounted.current = false;
+    };
+  }, []);
+  useEffect(() => {
+    let alive = true;
+    let pending = true;
+    const request = nextRequestId();
+    const task = {
+      id: `directory-compare-${request}`,
+      title: tx("Comparing directories"),
+      message: null as string | null,
+      fraction: null as number | null,
+      cancel: () => {
+        void commands.cancelRequest(request);
+      },
+    };
+    cancel.current = task.cancel;
+    upsertTask({ ...task, done: false });
+    const channel = new Channel<DirectoryCompareProgress>();
+    channel.onmessage = (p) => {
+      if (!alive) return;
+      setProgress(p);
+      task.message = p.path;
+      task.fraction = p.total ? p.compared / p.total : null;
+      upsertTask({ ...task, done: false });
+    };
+    void call(commands.fsCompareDirectories(left, right, request, channel))
+      .then((rows) => {
+        if (!alive) return;
+        setEntries(rows);
+        setCurrent((prev) => rows.find((e) => e.path === prev?.path) ?? null);
+      })
+      .catch((e) => {
+        if (!alive) return;
+        if (isCancelled(e)) setCancelled(true);
+        else setError(e instanceof Error ? e.message : String(e));
+      })
+      .finally(() => {
+        pending = false;
+        upsertTask({ ...task, done: true });
+        if (alive) setBusy(false);
+      });
+    return () => {
+      alive = false;
+      if (pending) task.cancel();
+      upsertTask({ ...task, done: true });
+    };
+  }, [left, right, generation]);
+
+  const visible = useMemo(() => {
+    const paths = new Set<string>();
+    const query = filter.trim().toLocaleLowerCase();
+    for (const e of entries) {
+      if ((!showEqual && e.status === "equal") || !e.path.toLocaleLowerCase().includes(query)) continue;
+      let path = e.path;
+      while (path) {
+        paths.add(path);
+        const slash = path.lastIndexOf("/");
+        path = slash < 0 ? "" : path.slice(0, slash);
+      }
+    }
+    return entries.filter((e) => paths.has(e.path));
+  }, [entries, showEqual, filter]);
+  const tree = useMemo(() => buildFileTree(visible, (e) => e.path, directory), [visible]);
+  const selected = cancelled || error ? null : (visible.find((e) => e.path === current?.path) ?? null);
+  const diff = selected && directoryDiff(left, right, selected);
+  const refresh = () => {
+    setBusy(true);
+    setCancelled(false);
+    setError(null);
+    setProgress(null);
+    setGeneration((g) => g + 1);
+  };
+
+  const operate = async (side: "left" | "right" | "delete") => {
+    if (!selected || busy || operating) return;
+    setOperating(true);
+    setOperationError(null);
+    let attempted = false;
+    const targetRoot = side === "left" ? left : right;
+    try {
+      if (side === "delete") {
+        if (!!selected.leftKind === !!selected.rightKind) return;
+        const path = join(selected.leftKind ? left : right, selected.path);
+        if (!(await confirmDialog({ title: "Delete", message: tx`Delete ${path}?`, okLabel: "Delete", danger: true })))
+          return;
+        attempted = true;
+        await call(commands.fsDelete(path));
+        notifyFileOperation({ kind: "deleted", paths: [path] });
+        emitLocalIdeEvent({ type: "fsChanged", created: [], modified: [], removed: [path] });
+      } else {
+        const sourceRoot = side === "left" ? right : left;
+        const to = join(targetRoot, selected.path);
+        try {
+          attempted = true;
+          await call(commands.fsCopyMerge(sourceRoot, targetRoot, selected.path, false));
+        } catch (e) {
+          if (!(e instanceof IpcError) || e.kind !== "alreadyExists") throw e;
+          if (
+            !(await confirmDialog({
+              title: "Overwrite files?",
+              message: tx`Copy to ${to} and overwrite existing files?`,
+              okLabel: "Overwrite",
+              danger: true,
+            }))
+          )
+            return;
+          await call(commands.fsCopyMerge(sourceRoot, targetRoot, selected.path, true));
+        }
+        notifyFileOperation({ kind: "created", paths: [to] });
+        emitLocalIdeEvent({ type: "fsChanged", created: [to], modified: [to], removed: [] });
+      }
+    } catch (e) {
+      if (mounted.current) setOperationError(e instanceof Error ? e.message : String(e));
+    } finally {
+      if (mounted.current) {
+        setOperating(false);
+        if (attempted) refresh();
+      }
+    }
+  };
+
+  return (
+    <Dialog
+      open
+      title="Compare Directories"
+      onClose={onClose}
+      width={diff ? 1100 : 780}
+      buttons={[
+        {
+          label: "Show Diff",
+          disabled: !diff || busy || operating,
+          onClick: () => {
+            if (diff) {
+              void openDiff(diff);
+              onClose();
+            }
+          },
+        },
+        { label: "Close", role: "cancel" },
+      ]}
+    >
+      <div className={styles.compareNotice}>{tx`Left: ${left}`}</div>
+      <div className={styles.compareNotice}>{tx`Right: ${right}`}</div>
+      <div className={styles.compareToolbar}>
+        <Input
+          aria-label="Filter by name"
+          placeholder="Filter by name"
+          value={filter}
+          onChange={(e) => setFilter(e.target.value)}
+        />
+        <Checkbox label="Show identical files" checked={showEqual} onChange={setShowEqual} />
+        <Button size="small" disabled={busy || operating} onClick={refresh}>
+          Refresh
+        </Button>
+      </div>
+      <div className={styles.compareToolbar}>
+        <Button size="small" disabled={!selected?.rightKind || busy || operating} onClick={() => void operate("left")}>
+          Copy to Left
+        </Button>
+        <Button size="small" disabled={!selected?.leftKind || busy || operating} onClick={() => void operate("right")}>
+          Copy to Right
+        </Button>
+        <Button
+          size="small"
+          disabled={!selected || !!selected.leftKind === !!selected.rightKind || busy || operating}
+          onClick={() => void operate("delete")}
+        >
+          Delete
+        </Button>
+        {operating && <Spinner size={14} />}
+      </div>
+      {error && (
+        <div className={styles.error} role="alert">
+          {tx(error)}
+        </div>
+      )}
+      {operationError && (
+        <div className={styles.error} role="alert">
+          {tx(operationError)}
+        </div>
+      )}
+      {busy && (
+        <div className={styles.compareToolbar} role="status">
+          <Spinner size={14} />
+          <span>
+            {progress?.total != null
+              ? tx`Compared ${progress.compared} of ${progress.total} entries`
+              : tx`Scanned ${progress?.scanned ?? 0} entries`}
+          </span>
+          <Button size="small" onClick={() => cancel.current()}>
+            Cancel
+          </Button>
+        </div>
+      )}
+      {cancelled && (
+        <div className={styles.compareNotice} role="status">
+          <T>Comparison cancelled</T>
+        </div>
+      )}
+      {!busy && !cancelled && !error && !visible.length && (
+        <div className={styles.empty} role="status">
+          <T>No matching differences</T>
+        </div>
+      )}
+      {!!tree.length && (
+        <ComparisonTree
+          tree={tree}
+          current={busy || operating ? null : selected}
+          onSelect={setCurrent}
+          diffFor={(e) => directoryDiff(left, right, e)}
+          openOnActivate={!busy && !operating}
+          onOpen={onClose}
+          ariaLabel="Compared files"
+          renderDetails={(n) => {
+            const entry = n.file ?? n.directory;
+            return <span className={styles.fileDir}>{entry ? tx(STATUS[entry.status]) : n.count}</span>;
+          }}
+        />
+      )}
+    </Dialog>
+  );
+}
diff --git a/src/features/vcs/__tests__/diffToolbar.test.tsx b/src/features/vcs/__tests__/diffToolbar.test.tsx
index 9bd19206f..dbf74852f 100644
--- a/src/features/vcs/__tests__/diffToolbar.test.tsx
+++ b/src/features/vcs/__tests__/diffToolbar.test.tsx
@@ -66,6 +66,21 @@ beforeEach(() => {
 });
 
 describe("Diff toolbar", () => {
+  it("shows a binary notice for disk comparisons instead of identical empty text", async () => {
+    probe.mockResolvedValue({ status: "ok", data: { size: 3, binary: true, tooLarge: false } });
+    const binaryInput = {
+      ...input,
+      data: { path: "/p/right.bin", left: { type: "file", path: "/p/left.bin" }, right: { type: "worktree" } },
+    } as EditorInput;
+    render(<DiffEditor input={binaryInput} />);
+    expect(await screen.findByText("Binary files cannot be shown as text")).toBeInTheDocument();
+    expect(screen.queryByText("Contents are identical")).toBeNull();
+    expect(screen.queryByRole("region", { name: /left.bin/ })).toBeNull();
+    probe.mockResolvedValue({ status: "ok", data: { size: 3, binary: false, tooLarge: false } });
+    fireEvent.click(screen.getByRole("button", { name: "Refresh" }));
+    await waitFor(() => expect(screen.queryByText("Binary files cannot be shown as text")).toBeNull());
+  });
+
   it("puts Jump to Source right after Next Difference, in the navigation group", async () => {
     render(<DiffEditor input={input} />);
     await screen.findByRole("button", { name: "Jump to Source" });
diff --git a/src/features/vcs/__tests__/directoryCompare.test.tsx b/src/features/vcs/__tests__/directoryCompare.test.tsx
new file mode 100644
index 000000000..896fc57e1
--- /dev/null
+++ b/src/features/vcs/__tests__/directoryCompare.test.tsx
@@ -0,0 +1,179 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { cleanup, fireEvent, render, screen, waitFor } from "@testing-library/react";
+import type { DirectoryCompareEntry } from "@/bindings";
+
+const mocks = vi.hoisted(() => ({
+  compare: vi.fn(),
+  cancel: vi.fn(),
+  copy: vi.fn(),
+  remove: vi.fn(),
+  confirm: vi.fn(),
+  open: vi.fn(),
+}));
+vi.mock("@/platform/ipc", async (original) => {
+  const real = await original<typeof import("@/platform/ipc")>();
+  return {
+    ...real,
+    commands: {
+      ...real.commands,
+      fsCompareDirectories: mocks.compare,
+      fsCopyMerge: mocks.copy,
+      fsDelete: mocks.remove,
+      cancelRequest: mocks.cancel,
+    },
+  };
+});
+vi.mock("@tauri-apps/api/core", async (original) => ({
+  ...(await original<typeof import("@tauri-apps/api/core")>()),
+  Channel: class {
+    onmessage = () => {};
+  },
+}));
+vi.mock("../DiffEditor", () => ({
+  DiffEditor: ({ input }: { input: unknown }) => <div data-testid="diff">{JSON.stringify(input)}</div>,
+}));
+vi.mock("../dialogs", () => ({ confirmDialog: mocks.confirm, openDialog: vi.fn(), promptText: vi.fn() }));
+vi.mock("../diffInput", async (original) => ({
+  ...(await original<typeof import("../diffInput")>()),
+  openDiff: mocks.open,
+}));
+import { DirectoryCompareDialog, directoryDiff } from "../DirectoryCompare";
+
+const row = (
+  path: string,
+  status: DirectoryCompareEntry["status"],
+  leftKind: DirectoryCompareEntry["leftKind"] = "file",
+  rightKind: DirectoryCompareEntry["rightKind"] = "file",
+): DirectoryCompareEntry => ({ path, status, leftKind, rightKind });
+const rows = [
+  row("nested", "different", "dir", "dir"),
+  row("nested/中文.txt", "different"),
+  row("only-left.txt", "leftOnly", "file", null),
+  row("only-right.txt", "rightOnly", null, "file"),
+  row("same.txt", "equal"),
+  row("empty", "leftOnly", "dir", null),
+];
+const ok = (data: unknown = null) => ({ status: "ok", data });
+const setup = () => render(<DirectoryCompareDialog left="/p/left" right="/p/right" onClose={() => {}} />);
+
+beforeEach(() => {
+  vi.clearAllMocks();
+  mocks.compare.mockResolvedValue(ok(rows));
+  mocks.copy.mockResolvedValue(ok());
+  mocks.remove.mockResolvedValue(ok());
+  mocks.confirm.mockResolvedValue(true);
+});
+afterEach(cleanup);
+
+describe("disk directory comparison", () => {
+  it("reuses the changes tree, filters names and toggles identical files", async () => {
+    setup();
+    expect(await screen.findByText("中文.txt")).toBeInTheDocument();
+    expect(screen.getAllByText("Only on left")).toHaveLength(2);
+    expect(screen.getByText("Only on right")).toBeInTheDocument();
+    expect(screen.queryByText("same.txt")).toBeNull();
+    fireEvent.click(screen.getByRole("checkbox", { name: "Show identical files" }));
+    expect(screen.getByText("same.txt")).toBeInTheDocument();
+    fireEvent.change(screen.getByRole("textbox", { name: "Filter by name" }), { target: { value: "中文" } });
+    expect(screen.queryByText("same.txt")).toBeNull();
+    expect(screen.getByText("nested")).toBeInTheDocument();
+    fireEvent.mouseDown(screen.getByText("nested"), { button: 0 });
+    expect(screen.getByRole("button", { name: "Copy to Right" })).toBeEnabled();
+  });
+
+  it("previews on selection and opens the existing diff on double click, including missing sides", async () => {
+    setup();
+    fireEvent.mouseDown(await screen.findByText("中文.txt"), { button: 0 });
+    expect(screen.getByTestId("diff")).toHaveTextContent("/p/left/nested/中文.txt");
+    fireEvent.doubleClick(screen.getByText("中文.txt"));
+    expect(mocks.open).toHaveBeenCalledWith(expect.objectContaining({ path: "/p/right/nested/中文.txt" }));
+    expect(directoryDiff("/l", "/r", rows[2]!)?.right.type).toBe("text");
+    expect(directoryDiff("/l", "/r", rows[3]!)?.left.type).toBe("text");
+    expect(directoryDiff("/l", "/r", row("type", "different", "file", "dir"))).toBeNull();
+    expect(
+      directoryDiff("/l", "/r", {
+        ...row("link", "different", "symlink", "symlink"),
+        leftLink: "one",
+        rightLink: "two",
+      }),
+    ).toMatchObject({
+      left: { type: "text", text: "one" },
+      right: { type: "text", text: "two" },
+    });
+  });
+
+  it.each(["Copy to Left", "Copy to Right"])(
+    "confirms before overwriting, refreshes and restores selection after %s",
+    async (label) => {
+      mocks.copy
+        .mockResolvedValueOnce({ status: "error", error: { kind: "alreadyExists", message: "exists" } })
+        .mockResolvedValueOnce(ok());
+      setup();
+      fireEvent.mouseDown(await screen.findByText("中文.txt"), { button: 0 });
+      fireEvent.click(screen.getByRole("button", { name: label }));
+      await waitFor(() =>
+        expect(mocks.confirm).toHaveBeenCalledWith(expect.objectContaining({ title: "Overwrite files?" })),
+      );
+      await waitFor(() => expect(mocks.compare).toHaveBeenCalledTimes(2));
+      expect(mocks.copy.mock.calls[0]![3]).toBe(false);
+      expect(mocks.copy.mock.calls[1]![3]).toBe(true);
+      expect(mocks.copy.mock.calls[0]!.slice(0, 3)).toEqual(
+        label === "Copy to Left"
+          ? ["/p/right", "/p/left", "nested/中文.txt"]
+          : ["/p/left", "/p/right", "nested/中文.txt"],
+      );
+      expect(screen.getByTestId("diff")).toBeInTheDocument();
+    },
+  );
+
+  it("does not overwrite when confirmation is declined and reports operation errors", async () => {
+    mocks.copy.mockResolvedValue({ status: "error", error: { kind: "alreadyExists", message: "exists" } });
+    mocks.confirm.mockResolvedValue(false);
+    setup();
+    fireEvent.mouseDown(await screen.findByText("中文.txt"), { button: 0 });
+    fireEvent.click(screen.getByRole("button", { name: "Copy to Right" }));
+    await waitFor(() => expect(mocks.compare).toHaveBeenCalledTimes(2));
+    expect(mocks.copy).toHaveBeenCalledTimes(1);
+    mocks.copy.mockResolvedValue({ status: "error", error: { kind: "permissionDenied", message: "Cannot write" } });
+    fireEvent.click(screen.getByRole("button", { name: "Copy to Right" }));
+    expect(await screen.findByRole("alert")).toHaveTextContent("Cannot write");
+  });
+
+  it("copies empty and nonempty subdirectories and confirms deletion only for one-sided entries", async () => {
+    setup();
+    fireEvent.mouseDown(await screen.findByText("nested"), { button: 0 });
+    expect(screen.getByRole("button", { name: "Delete" })).toBeDisabled();
+    fireEvent.click(screen.getByRole("button", { name: "Copy to Right" }));
+    await waitFor(() => expect(mocks.copy).toHaveBeenCalledWith("/p/left", "/p/right", "nested", false));
+    await waitFor(() => expect(mocks.compare).toHaveBeenCalledTimes(2));
+    fireEvent.mouseDown(screen.getByText("empty"), { button: 0 });
+    fireEvent.click(screen.getByRole("button", { name: "Copy to Right" }));
+    await waitFor(() => expect(mocks.copy).toHaveBeenCalledWith("/p/left", "/p/right", "empty", false));
+    await waitFor(() => expect(mocks.compare).toHaveBeenCalledTimes(3));
+    fireEvent.mouseDown(screen.getByText("only-left.txt"), { button: 0 });
+    mocks.confirm.mockResolvedValueOnce(false);
+    fireEvent.click(screen.getByRole("button", { name: "Delete" }));
+    await waitFor(() => expect(mocks.confirm).toHaveBeenCalled());
+    expect(mocks.remove).not.toHaveBeenCalled();
+    fireEvent.click(screen.getByRole("button", { name: "Delete" }));
+    await waitFor(() => expect(mocks.remove).toHaveBeenCalledWith("/p/left/only-left.txt"));
+  });
+
+  it("streams progress, cancels on demand and on close, and ignores stale results after refresh", async () => {
+    let resolve!: (value: unknown) => void;
+    mocks.compare.mockImplementationOnce((_l, _r, _request, channel) => {
+      channel.onmessage({ scanned: 20, compared: 5, total: 10, bytesRead: 100, path: "big" });
+      return new Promise((r) => {
+        resolve = r;
+      });
+    });
+    const view = setup();
+    expect(await screen.findByText("Compared 5 of 10 entries")).toBeInTheDocument();
+    const request = mocks.compare.mock.calls[0]![2];
+    fireEvent.click(screen.getByRole("button", { name: "Cancel" }));
+    expect(mocks.cancel).toHaveBeenCalledWith(request);
+    view.unmount();
+    expect(mocks.cancel).toHaveBeenCalledTimes(2);
+    resolve(ok(rows));
+  });
+});
diff --git a/src/features/vcs/__tests__/directoryCompareActions.test.ts b/src/features/vcs/__tests__/directoryCompareActions.test.ts
new file mode 100644
index 000000000..4a0d5cbae
--- /dev/null
+++ b/src/features/vcs/__tests__/directoryCompareActions.test.ts
@@ -0,0 +1,95 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+const mocks = vi.hoisted(() => ({
+  show: vi.fn(),
+  read: vi.fn(),
+  notify: vi.fn(),
+  pick: vi.fn(),
+  remote: vi.fn(),
+  prompt: vi.fn(),
+  openDiff: vi.fn(),
+}));
+vi.mock("../DirectoryCompare", () => ({ showDirectoryComparison: mocks.show }));
+vi.mock("../dialogs", () => ({ promptText: mocks.prompt }));
+vi.mock("../diffInput", () => ({ openDiff: mocks.openDiff }));
+vi.mock("@tauri-apps/plugin-dialog", () => ({ open: mocks.pick }));
+vi.mock("@/platform/remote", () => ({ isRemoteWindow: mocks.remote }));
+vi.mock("@/platform/ipc", async (original) => ({
+  ...(await original<typeof import("@/platform/ipc")>()),
+  isTauri: () => true,
+  commands: { fsEntryKind: mocks.read },
+}));
+vi.mock("@/workbench/contributions", async (original) => ({
+  ...(await original<typeof import("@/workbench/contributions")>()),
+  notifications: () => ({ notify: mocks.notify }),
+}));
+import { getAction, isActionEnabled } from "@/platform/actions";
+import { provideProjectViewSelection } from "@/workbench/contributions";
+import { registerCompareActions } from "../compare";
+
+let dispose: () => void;
+beforeEach(() => {
+  vi.clearAllMocks();
+  dispose = registerCompareActions();
+  mocks.remote.mockReturnValue(false);
+  mocks.read.mockImplementation((path: string) =>
+    Promise.resolve({ status: "ok", data: path.endsWith(".txt") ? "file" : "dir" }),
+  );
+});
+afterEach(() => dispose());
+
+describe("directory compare actions", () => {
+  it("has a stable searchable action and resolves the selection for Find Action", async () => {
+    const unselect = provideProjectViewSelection(() => ["/p/left", "/p/right"]);
+    try {
+      const action = getAction("diff.compareDirectories")!;
+      expect(action.title).toBe("Compare Directories");
+      expect(action.hidden).not.toBe(true);
+      expect(isActionEnabled(action, { projectOpen: true })).toBe(true);
+      await action.run({ ctx: { projectOpen: true } });
+      expect(mocks.show).toHaveBeenCalledWith("/p/left", "/p/right");
+      await action.run({ ctx: { projectOpen: true }, arg: { paths: ["/x/left", "/x/right"] } });
+      expect(mocks.show).toHaveBeenLastCalledWith("/x/left", "/x/right");
+    } finally {
+      unselect();
+    }
+  });
+
+  it("rejects mixed selections and does not start a directory comparison", async () => {
+    await getAction("diff.compareDirectories")!.run({ ctx: {}, arg: ["/p/left", "/p/file.txt"] });
+    expect(mocks.show).not.toHaveBeenCalled();
+    expect(mocks.notify).toHaveBeenCalledWith(expect.objectContaining({ title: "Select two directories to compare" }));
+  });
+
+  it("uses the native folder picker for Compare With on a local directory", async () => {
+    mocks.pick.mockResolvedValue("/p/right");
+    await getAction("diff.compareWith")!.run({ ctx: {}, arg: { path: "/p/left", directory: true } });
+    expect(mocks.pick).toHaveBeenCalledWith(expect.objectContaining({ directory: true }));
+    expect(mocks.show).toHaveBeenCalledWith("/p/left", "/p/right");
+    expect(mocks.openDiff).not.toHaveBeenCalled();
+  });
+
+  it("uses remote paths and validates the selected directory via the routed filesystem", async () => {
+    mocks.remote.mockReturnValue(true);
+    mocks.prompt.mockResolvedValue({ value: "/remote/right" });
+    const unselect = provideProjectViewSelection(() => ["/remote/left"]);
+    try {
+      await getAction("diff.compareWith")!.run({ ctx: {} });
+      expect(mocks.prompt).toHaveBeenCalledWith(
+        expect.objectContaining({ label: "Directory path", initial: "/remote/left" }),
+      );
+      expect(mocks.pick).not.toHaveBeenCalled();
+      expect(mocks.read).toHaveBeenCalledWith("/remote/right");
+      expect(mocks.show).toHaveBeenCalledWith("/remote/left", "/remote/right");
+    } finally {
+      unselect();
+    }
+  });
+
+  it("leaves file Compare With on the existing diff flow", async () => {
+    mocks.pick.mockResolvedValue("/p/b.txt");
+    await getAction("diff.compareWith")!.run({ ctx: {}, arg: "/p/a.txt" });
+    expect(mocks.pick).toHaveBeenCalledWith(expect.objectContaining({ directory: false }));
+    expect(mocks.openDiff).toHaveBeenCalledWith(expect.objectContaining({ path: "/p/b.txt" }));
+    expect(mocks.show).not.toHaveBeenCalled();
+  });
+});
diff --git a/src/features/vcs/__tests__/fileTree.test.ts b/src/features/vcs/__tests__/fileTree.test.ts
index c0327edca..158f32829 100644
--- a/src/features/vcs/__tests__/fileTree.test.ts
+++ b/src/features/vcs/__tests__/fileTree.test.ts
@@ -9,4 +9,21 @@ describe("buildFileTree", () => {
     expect(tree[1]!.children.map((c) => c.name)).toEqual(["a.ts", "b.ts"]);
     expect(dirKeys(tree)).toEqual(["d:docs/x/y", "d:src/app"]);
   });
+
+  it("retains explicit empty directories and their entries for subtree operations", () => {
+    const entries = [
+      { path: "empty", dir: true },
+      { path: "src", dir: true },
+      { path: "src/nested", dir: true },
+      { path: "src/nested/a", dir: false },
+    ];
+    const tree = buildFileTree(
+      entries,
+      (e) => e.path,
+      (e) => e.dir,
+    );
+    expect(tree[0]).toMatchObject({ name: "empty", directory: entries[0], children: [], count: 0 });
+    expect(tree[1]).toMatchObject({ name: "src", directory: entries[1] });
+    expect(tree[1]!.children[0]).toMatchObject({ name: "nested", directory: entries[2] });
+  });
 });
diff --git a/src/features/vcs/common.module.css b/src/features/vcs/common.module.css
index c18a071e9..9e9acc8df 100644
--- a/src/features/vcs/common.module.css
+++ b/src/features/vcs/common.module.css
@@ -310,6 +310,17 @@
   color: var(--fg-subtle);
   overflow-wrap: anywhere;
 }
+.compareToolbar {
+  display: flex;
+  align-items: center;
+  flex-wrap: wrap;
+  gap: 8px;
+  padding: 6px 14px;
+}
+.compareToolbar > input {
+  flex: 1;
+  min-width: 140px;
+}
 .compareAdded {
   color: var(--vcs-added);
   font-variant-numeric: tabular-nums;
diff --git a/src/features/vcs/compare.tsx b/src/features/vcs/compare.tsx
index a2799e617..1437abdbe 100644
--- a/src/features/vcs/compare.tsx
+++ b/src/features/vcs/compare.tsx
@@ -4,10 +4,13 @@
  */
 import { activeEditor } from "@/editor/api";
 import { registerActions } from "@/platform/actions";
-import { isTauri } from "@/platform/ipc";
-import { useProject } from "@/platform/project";
-import { maybeEditorService, notifications } from "@/workbench/contributions";
+import { call, commands, isTauri } from "@/platform/ipc";
+import { isRemoteWindow } from "@/platform/remote";
+import { maybeEditorService, notifications, projectViewSelection } from "@/workbench/contributions";
+import { promptText } from "./dialogs";
 import { focusedDiffNavigator } from "./diffNavigator";
+import { compareFilesData, displayPath } from "./compareData";
+export { compareFilesData, displayPath } from "./compareData";
 import { openDiff, type DiffData } from "./diffInput";
 import { baseName } from "./model";
 import { tx } from "@/platform/i18n";
@@ -27,20 +30,6 @@ function argPaths(arg: unknown): string[] {
   return p ? [p] : [];
 }
 
-/** Project-relative path for labels. */
-export function displayPath(path: string, root = useProject.getState().project?.root ?? null): string {
-  return root && path.startsWith(root + "/") ? path.slice(root.length + 1) : path;
-}
-
-/** Diff of two files on disk; both sides are live, editable documents. */
-export function compareFilesData(leftPath: string, rightPath: string): DiffData {
-  return {
-    path: rightPath,
-    left: { type: "file", path: leftPath, label: displayPath(leftPath) },
-    right: { type: "worktree", label: displayPath(rightPath) },
-  };
-}
-
 /** Clipboard ↔ the file (editable) or ↔ the editor selection. */
 export function clipboardDiffData(path: string, clipboard: string, selection: string | null): DiffData {
   return {
@@ -122,6 +111,29 @@ async function pickComparison(
 
 const contextPath = (arg: unknown) => argPath(arg) ?? maybeEditorService()?.activePath() ?? undefined;
 
+async function showDirectories(left: string, right: string) {
+  const { showDirectoryComparison } = await import("./DirectoryCompare");
+  showDirectoryComparison(left, right);
+}
+
+async function isDirectory(path: string): Promise<boolean> {
+  try {
+    return (await call(commands.fsEntryKind(path))) === "dir";
+  } catch {
+    return false;
+  }
+}
+
+async function pickDirectory(near: string): Promise<string | null> {
+  if (isRemoteWindow() || !isTauri()) {
+    const picked = await promptText({ title: "Compare With", label: "Directory path", initial: near, mono: true });
+    return picked?.value ?? null;
+  }
+  const { open } = await import("@tauri-apps/plugin-dialog");
+  const picked = await open({ multiple: false, directory: true, title: tx("Compare With"), defaultPath: near });
+  return (Array.isArray(picked) ? picked[0] : picked) ?? null;
+}
+
 export function registerCompareActions(): () => void {
   return registerActions([
     {
@@ -210,10 +222,18 @@ export function registerCompareActions(): () => void {
       category: "Diff",
       icon: "diff",
       when: "projectOpen",
-      keywords: ["diff", "compare files"],
+      keywords: ["diff", "compare files", "compare folders"],
       run: async ({ arg }) => {
-        const path = contextPath(arg);
+        const path = argPath(arg) ?? projectViewSelection()[0] ?? contextPath(arg);
         if (!path) return info("Open or select a file to compare");
+        const directoryArg = !!arg && typeof arg === "object" && "directory" in arg && arg.directory === true;
+        if (directoryArg || (isTauri() && (await isDirectory(path)))) {
+          const other = await pickDirectory(path);
+          if (!other || other === path) return;
+          if (!(await isDirectory(other))) return info("Select a directory to compare");
+          await showDirectories(path, other);
+          return;
+        }
         const other = await pickComparison(path);
         if (!other) return;
         if (other.type === "file") {
@@ -228,6 +248,20 @@ export function registerCompareActions(): () => void {
         }
       },
     },
+    {
+      id: "diff.compareDirectories",
+      title: "Compare Directories",
+      category: "Diff",
+      icon: "diff",
+      when: "projectOpen",
+      keywords: ["diff", "folders", "compare folders"],
+      run: async ({ arg }) => {
+        const paths = arg === undefined ? projectViewSelection() : argPaths(arg);
+        if (paths.length !== 2 || !(await isDirectory(paths[0]!)) || !(await isDirectory(paths[1]!)))
+          return info("Select two directories to compare");
+        await showDirectories(paths[0]!, paths[1]!);
+      },
+    },
     {
       id: "diff.compareFiles",
       title: "Compare Files",
diff --git a/src/features/vcs/compareData.ts b/src/features/vcs/compareData.ts
new file mode 100644
index 000000000..fc693fce1
--- /dev/null
+++ b/src/features/vcs/compareData.ts
@@ -0,0 +1,16 @@
+import { useProject } from "@/platform/project";
+import type { DiffData } from "./diffInput";
+
+/** Project-relative path for labels. */
+export function displayPath(path: string, root = useProject.getState().project?.root ?? null): string {
+  return root && path.startsWith(root + "/") ? path.slice(root.length + 1) : path;
+}
+
+/** Diff of two files on disk; both sides are live, editable documents. */
+export function compareFilesData(leftPath: string, rightPath: string): DiffData {
+  return {
+    path: rightPath,
+    left: { type: "file", path: leftPath, label: displayPath(leftPath) },
+    right: { type: "worktree", label: displayPath(rightPath) },
+  };
+}
diff --git a/src/features/vcs/fileTree.ts b/src/features/vcs/fileTree.ts
index a31265634..72bd576fb 100644
--- a/src/features/vcs/fileTree.ts
+++ b/src/features/vcs/fileTree.ts
@@ -5,15 +5,22 @@ export interface FileTreeNode<F> {
   /** Directory label (`src/app`) or file name. */
   name: string;
   file: F | null;
+  /** An explicit directory entry, including empty directories. */
+  directory?: F;
   children: FileTreeNode<F>[];
   /** Number of files below (1 for a file). */
   count: number;
 }
 
-export function buildFileTree<F>(files: readonly F[], relPath: (f: F) => string): FileTreeNode<F>[] {
+export function buildFileTree<F>(
+  files: readonly F[],
+  relPath: (f: F) => string,
+  isDirectory?: (f: F) => boolean,
+): FileTreeNode<F>[] {
   interface Dir {
     dirs: Map<string, Dir>;
     files: { name: string; file: F; rel: string }[];
+    entry?: F;
   }
   const root: Dir = { dirs: new Map(), files: [] };
   for (const f of files) {
@@ -26,7 +33,11 @@ export function buildFileTree<F>(files: readonly F[], relPath: (f: F) => string)
       if (!next) d.dirs.set(p, (next = { dirs: new Map(), files: [] }));
       d = next;
     }
-    d.files.push({ name, file: f, rel });
+    if (isDirectory?.(f)) {
+      let sub = d.dirs.get(name);
+      if (!sub) d.dirs.set(name, (sub = { dirs: new Map(), files: [] }));
+      sub.entry = f;
+    } else d.files.push({ name, file: f, rel });
   }
 
   const convert = (d: Dir, prefix: string): FileTreeNode<F>[] => {
@@ -35,7 +46,7 @@ export function buildFileTree<F>(files: readonly F[], relPath: (f: F) => string)
       let label = name;
       let path = prefix ? `${prefix}/${name}` : name;
       let cur = sub;
-      while (cur.files.length === 0 && cur.dirs.size === 1) {
+      while (!cur.entry && cur.files.length === 0 && cur.dirs.size === 1) {
         const [n, only] = [...cur.dirs][0]!;
         label += `/${n}`;
         path += `/${n}`;
@@ -46,6 +57,7 @@ export function buildFileTree<F>(files: readonly F[], relPath: (f: F) => string)
         key: `d:${path}`,
         name: label,
         file: null,
+        directory: cur.entry,
         children,
         count: children.reduce((n, c) => n + c.count, 0),
       });
diff --git a/src/features/vcs/operations.tsx b/src/features/vcs/operations.tsx
index e0099acd0..b18a7ae1d 100644
--- a/src/features/vcs/operations.tsx
+++ b/src/features/vcs/operations.tsx
@@ -8,7 +8,7 @@ import { useEffect, useMemo, useState } from "react";
 import type { ChangedFile, Commit, CompareResult, ResetMode, WorkingTreeChange } from "@/bindings";
 import { executeAction } from "@/platform/actions";
 import { call, commands, nextRequestId } from "@/platform/ipc";
-import { Checkbox, Dialog, Icon, Input, Tree, Spinner, fileIconName, T } from "@/ui";
+import { Checkbox, Dialog, Icon, Input, Spinner, T } from "@/ui";
 import { notifications } from "@/workbench/contributions";
 import { diffInput, openDiff, type DiffData, type DiffSide } from "./diffInput";
 import { openDialog, promptText } from "./dialogs";
@@ -17,10 +17,10 @@ import { runGitOperation, runOp } from "./ops";
 import { reloadLog, useGitLog } from "./logStore";
 import { conflictedFiles, currentRepo, currentRepoRoot, refreshNow, repoName, repoOf, useVcs } from "./store";
 import styles from "./common.module.css";
-import { DiffEditor } from "./DiffEditor";
-import { buildFileTree, dirKeys, type FileTreeNode } from "./fileTree";
+import { ComparisonTree } from "./ComparisonTree";
+import { buildFileTree, type FileTreeNode } from "./fileTree";
 import { tx } from "@/platform/i18n";
-import { displayPath } from "./compare";
+import { displayPath } from "./compareData";
 
 // ---------------------------------------------------------------------------
 // Operation in progress
@@ -528,8 +528,6 @@ export function ChangesBetweenDialog({
   const [files, setFiles] = useState<ComparisonFile[] | null>(null);
   const [result, setResult] = useState<CompareResult | null>(null);
   const [error, setError] = useState<string | null>(null);
-  const [selected, setSelected] = useState<ReadonlySet<string>>(new Set());
-  const [expanded, setExpanded] = useState<ReadonlySet<string> | null>(null);
   const [current, setCurrent] = useState<ComparisonFile | null>(null);
   const fromRev = from.rev;
   const toRev = to?.rev ?? null;
@@ -665,52 +663,25 @@ export function ChangesBetweenDialog({
         </div>
       ) : null}
       {files && files.length > 0 ? (
-        <div className={`${styles.comparison} ${input ? styles.comparisonWithDiff : ""}`}>
-          <Tree<FileTreeNode<ComparisonFile>>
-            roots={tree}
-            getKey={(n) => n.key}
-            getLabel={(n) => n.name}
-            getChildren={(n) => (n.file ? undefined : n.children)}
-            isExpandable={(n) => !n.file}
-            expanded={expanded ?? new Set(dirKeys(tree))}
-            onExpandedChange={setExpanded}
-            selected={selected}
-            onSelectionChange={(sel, lead) => {
-              setSelected(sel);
-              if (lead?.file) setCurrent(lead.file);
-            }}
-            onActivate={(n) => n.file && setCurrent(n.file)}
-            aria-label="Changed files"
-            className={styles.comparisonTree}
-            renderNode={(n) => (
-              <span className={styles.fileRow} style={{ flex: 1, padding: 0 }} title={n.file ? n.file.path : n.name}>
-                <Icon name={n.file ? fileIconName(n.name) : "folder"} size={14} />
-                <span
-                  className={styles.fileName}
-                  style={
-                    n.file ? { color: KIND_COLOR[n.file.kind === "untracked" ? "added" : n.file.kind] } : undefined
-                  }
-                >
-                  {n.name}
-                </span>
-                {n.file ? (
-                  <>
-                    <span className={styles.fileDir}>{tx(n.file.kind)}</span>
-                    {n.file.added !== undefined && <span className={styles.compareAdded}>+{n.file.added}</span>}
-                    {n.file.removed !== undefined && <span className={styles.compareRemoved}>−{n.file.removed}</span>}
-                  </>
-                ) : (
-                  <span className={styles.fileDir}>{n.count}</span>
-                )}
-              </span>
-            )}
-          />
-          {input && (
-            <div className={styles.comparisonDiff}>
-              <DiffEditor key={input.key} input={input} />
-            </div>
-          )}
-        </div>
+        <ComparisonTree
+          tree={tree}
+          current={current}
+          onSelect={setCurrent}
+          diffFor={diffFor}
+          getColor={(f) => KIND_COLOR[f.kind === "untracked" ? "added" : f.kind]}
+          ariaLabel="Changed files"
+          renderDetails={(n) =>
+            n.file ? (
+              <>
+                <span className={styles.fileDir}>{tx(n.file.kind)}</span>
+                {n.file.added !== undefined && <span className={styles.compareAdded}>+{n.file.added}</span>}
+                {n.file.removed !== undefined && <span className={styles.compareRemoved}>−{n.file.removed}</span>}
+              </>
+            ) : (
+              <span className={styles.fileDir}>{n.count}</span>
+            )
+          }
+        />
       ) : null}
     </Dialog>
   );
diff --git a/src/features/viewers/markdown/mermaid.ts b/src/features/viewers/markdown/mermaid.ts
index 903d190ca..cce3cca23 100644
--- a/src/features/viewers/markdown/mermaid.ts
+++ b/src/features/viewers/markdown/mermaid.ts
@@ -3,6 +3,7 @@
  * `[data-mermaid]` placeholder holding the source in `pre > code`; this module
  * turns placeholders into SVG. The library is imported on first use only.
  */
+import { fontsLoaded } from "@/platform/fonts";
 import type { Mermaid } from "mermaid";
 import { resolveTokenColor, toRgb } from "@/platform/cssColor";
 import { attachPanZoom } from "../panZoom";
@@ -32,7 +33,9 @@ function loadMermaid(): Promise<Mermaid> {
 export function themeKey(): string {
   const root = document.documentElement;
   const { theme = "", contrast = "", colorTheme = "", pluginTheme = "" } = root.dataset;
-  return `${theme}|${contrast}|${colorTheme}|${pluginTheme}|${root.style.getPropertyValue("--accent")}`;
+  const accent = root.style.getPropertyValue("--accent");
+  const font = getComputedStyle(root).getPropertyValue("--font-ui");
+  return `${theme}|${contrast}|${colorTheme}|${pluginTheme}|${accent}|${font}`;
 }
 
 /** Calls `cb` when the theme attributes (a plugin theme's included) or the accent on the root change. */
@@ -102,6 +105,7 @@ function removeTemp(id: string) {
 
 async function renderOne(source: string, key: string): Promise<Result> {
   const mermaid = await loadMermaid();
+  await fontsLoaded(getComputedStyle(document.documentElement).getPropertyValue("--font-ui").trim(), 16);
   configure(mermaid, key);
   const id = `openidea-mermaid-${++seq}`;
   try {
diff --git a/src/platform/candidateFonts.test.ts b/src/platform/candidateFonts.test.ts
index e9ea10c02..a83cb22d5 100644
--- a/src/platform/candidateFonts.test.ts
+++ b/src/platform/candidateFonts.test.ts
@@ -18,8 +18,26 @@ it("probes the legacy list and classifies measured mono and proportional familie
   ]);
 });
 it("returns no inferred families when Canvas is absent", () => {
+  const remove = vi.spyOn(HTMLCanvasElement.prototype, "remove");
   vi.spyOn(HTMLCanvasElement.prototype, "getContext").mockReturnValue(null);
   expect(detectCandidateFonts()).toEqual([]);
+  expect(remove).toHaveBeenCalledOnce();
+});
+it("detects user-installed candidates with a connected probe and removes it afterwards", () => {
+  const probes: HTMLCanvasElement[] = [];
+  vi.spyOn(HTMLCanvasElement.prototype, "getContext").mockImplementation(function (this: HTMLCanvasElement) {
+    probes.push(this);
+    const isConnected = () => this.isConnected;
+    return {
+      font: "",
+      measureText(this: { font: string }) {
+        return { width: isConnected() && this.font.includes('"Fira Code"') ? 120 : 100 };
+      },
+    } as unknown as CanvasRenderingContext2D;
+  });
+  expect(detectCandidateFonts()).toEqual([{ name: "Fira Code", monospaced: true }]);
+  expect(probes[0]?.hidden).toBe(true);
+  expect(probes[0]?.isConnected).toBe(false);
 });
 it("contains failures from Canvas and never claims candidates are installed", () => {
   vi.spyOn(HTMLCanvasElement.prototype, "getContext").mockImplementation(() => {
diff --git a/src/platform/candidateFonts.ts b/src/platform/candidateFonts.ts
index e566fc36c..72d9d8970 100644
--- a/src/platform/candidateFonts.ts
+++ b/src/platform/candidateFonts.ts
@@ -3,7 +3,7 @@
  * can miss installed families and are only hints; they say nothing about coverage.
  */
 import type { FontFamily } from "@/bindings";
-import { monoFontFamily } from "./fonts";
+import { createFontProbeCanvas, quoteFontFamily } from "./fonts";
 
 // Keep the former editor's 31 candidates for recovery, not as an installed-font whitelist.
 const CANDIDATES = [
@@ -41,9 +41,11 @@ const CANDIDATES = [
 ];
 
 export function detectCandidateFonts(): FontFamily[] {
+  let canvas: HTMLCanvasElement | undefined;
   try {
     if (typeof document === "undefined") return [];
-    const ctx = document.createElement("canvas").getContext("2d");
+    canvas = createFontProbeCanvas();
+    const ctx = canvas.getContext("2d");
     if (!ctx) return [];
     const width = (font: string, text: string) => {
       ctx.font = `32px ${font}`;
@@ -53,13 +55,13 @@ export function detectCandidateFonts(): FontFamily[] {
     const out: FontFamily[] = [];
     for (const name of CANDIDATES) {
       const present = ["monospace", "serif", "sans-serif"].some((base) => {
-        const measured = width(monoFontFamily(name, "", base), sample);
+        const measured = width(`${quoteFontFamily(name)}, ${base}`, sample);
         const baseline = width(base, sample);
         return Number.isFinite(measured) && Number.isFinite(baseline) && measured !== baseline;
       });
       if (!present) continue;
-      const narrow = width(monoFontFamily(name, "", "monospace"), "iiiiiiiiii");
-      const wide = width(monoFontFamily(name, "", "monospace"), "WWWWWWWWWW");
+      const narrow = width(`${quoteFontFamily(name)}, monospace`, "iiiiiiiiii");
+      const wide = width(`${quoteFontFamily(name)}, monospace`, "WWWWWWWWWW");
       out.push({
         name,
         monospaced: Number.isFinite(narrow) && Number.isFinite(wide) && Math.abs(narrow - wide) < 0.5,
@@ -70,5 +72,7 @@ export function detectCandidateFonts(): FontFamily[] {
     // Canvas can be absent or disabled in browser development / hardened webviews.
     // Never mark unmeasurable candidates as installed. The service adds bundled faces.
     return [];
+  } finally {
+    canvas?.remove();
   }
 }
diff --git a/src/platform/classFiles.test.ts b/src/platform/classFiles.test.ts
new file mode 100644
index 000000000..a7c869099
--- /dev/null
+++ b/src/platform/classFiles.test.ts
@@ -0,0 +1,34 @@
+import { describe, expect, it, vi } from "vitest";
+import { classFileBreakpointReason, isClassFile } from "./classFiles";
+import { isVirtualUri } from "./virtualDocs";
+import { canPlaceBreakpoint } from "@/features/debugger/breakpoints/languages";
+vi.mock("@/platform/workflowSettings", () => ({
+  workflowSettings: () => ({ debugger: { breakpointsAnyFile: true } }),
+}));
+
+describe("compiled class routing and breakpoint policy", () => {
+  it.each([
+    "/p/target/classes/p/C.class",
+    "/p/build/classes/java/main/p/C$1.class",
+    "C:\\p\\out\\C.class",
+    "file:///p/out/C.class",
+  ])("disables output breakpoints even with any-file enabled: %s", (path) => {
+    expect(isClassFile(path)).toBe(true);
+    expect(classFileBreakpointReason(path)).toBeTruthy();
+    expect(canPlaceBreakpoint("java", path)).toBe(false);
+  });
+  it.each([
+    "jdt://contents/a.jar/p/C.class?=p/a.jar%3Cp%28C.class",
+    "jdt://contents/a.jar/p/C.java?=p/a.jar%3Cp%28C.class",
+    "/p/src/main/java/p/C.java",
+  ])("keeps source and JDT breakpoints enabled: %s", (path) => {
+    expect(isClassFile(path)).toBe(false);
+    expect(classFileBreakpointReason(path)).toBeNull();
+    expect(canPlaceBreakpoint("java", path)).toBe(true);
+  });
+  it("treats disk class URIs as read-only server documents", () => {
+    expect(isVirtualUri("file:///p/out/C.class")).toBe(true);
+    expect(isVirtualUri("file:///p/src/C.java")).toBe(false);
+    expect(isClassFile("/m2/a.jar!/p/C.class")).toBe(true);
+  });
+});
diff --git a/src/platform/classFiles.ts b/src/platform/classFiles.ts
new file mode 100644
index 000000000..8af7e7351
--- /dev/null
+++ b/src/platform/classFiles.ts
@@ -0,0 +1,8 @@
+/** Compiled Java files are resolved before the binary viewer, at every opening entry. */
+export function isClassFile(path: string): boolean {
+  return !path.startsWith("jdt:") && /\.class$/i.test(path);
+}
+
+export function classFileBreakpointReason(path: string): string | null {
+  return isClassFile(path) ? "Breakpoints are not supported in output classes without source code." : null;
+}
diff --git a/src/platform/fonts.test.ts b/src/platform/fonts.test.ts
index 00f23c6de..65cf7520f 100644
--- a/src/platform/fonts.test.ts
+++ b/src/platform/fonts.test.ts
@@ -1,4 +1,4 @@
-import { describe, expect, it } from "vitest";
+import { afterEach, describe, expect, it, vi } from "vitest";
 import { monoFontFamily, quoteFontFamily, uiFontFamily } from "./fonts";
 
 const BASE = "var(--font-mono)";
@@ -36,10 +36,150 @@ it("escapes CSS special characters without turning a family into a list", () =>
 
 describe("uiFontFamily", () => {
   it.each([
-    ["Inter", '"Inter Variable", "Inter", system-ui, sans-serif'],
-    ["JetBrains Mono", '"JetBrains Mono Variable", "JetBrains Mono", system-ui, sans-serif'],
-    [' "PingFang SC" ', '"PingFang SC", system-ui, sans-serif'],
-  ])("%j", (family, expected) => {
-    expect(uiFontFamily(family)).toBe(expected);
+    ["Inter", "", '"Inter Variable", "Inter", system-ui, sans-serif'],
+    ["JetBrains Mono", "", '"JetBrains Mono Variable", "JetBrains Mono", system-ui, sans-serif'],
+    [' "PingFang SC" ', "", '"PingFang SC", system-ui, sans-serif'],
+    ["Inter", "思源黑体", '"Inter Variable", "Inter", "思源黑体", system-ui, sans-serif'],
+    ["Inter", " ", '"Inter Variable", "Inter", system-ui, sans-serif'],
+  ])("%j + %j", (family, fallback, expected) => {
+    expect(uiFontFamily(family, fallback)).toBe(expected);
+  });
+});
+
+describe("macOS user font resolver", () => {
+  afterEach(() => {
+    vi.unstubAllGlobals();
+    vi.restoreAllMocks();
+    vi.resetModules();
+  });
+
+  async function resolver(available: boolean | "symbols" | "connected", os = "macos") {
+    vi.resetModules();
+    const invoke = vi.fn();
+    vi.doMock("@tauri-apps/api/core", () => ({ isTauri: () => true, invoke }));
+    vi.doMock("./platformInfo", () => ({ guessOs: () => os }));
+    const canvases: HTMLCanvasElement[] = [];
+    vi.spyOn(HTMLCanvasElement.prototype, "getContext").mockImplementation(function (this: HTMLCanvasElement) {
+      const isConnected = () => this.isConnected;
+      canvases.push(this);
+      return {
+        font: "",
+        measureText(this: { font: string }, text: string) {
+          const covered =
+            available === true ||
+            (available === "symbols" && text.includes("\uF418")) ||
+            (available === "connected" && isConnected());
+          return { width: covered && this.font.includes('"') ? 200 : 100 };
+        },
+      } as unknown as CanvasRenderingContext2D;
+    });
+    const registered: { family: string; descriptors: unknown }[] = [];
+    vi.stubGlobal(
+      "FontFace",
+      class {
+        constructor(
+          public family: string,
+          _bytes: ArrayBuffer,
+          public descriptors: unknown,
+        ) {
+          registered.push(this);
+        }
+        load() {
+          return Promise.resolve(this);
+        }
+      },
+    );
+    const load = vi.fn().mockResolvedValue([]);
+    Object.defineProperty(document, "fonts", { configurable: true, value: { add: vi.fn(), delete: vi.fn(), load } });
+    const header = new TextEncoder().encode(
+      JSON.stringify([
+        { weight: 400, style: "normal", offset: 0, length: 2 },
+        { weight: 700, style: "normal", offset: 2, length: 2 },
+        { weight: 400, style: "italic", offset: 4, length: 2 },
+      ]),
+    );
+    const bundle = new Uint8Array(4 + header.length + 6);
+    new DataView(bundle.buffer).setUint32(0, header.length, true);
+    bundle.set(header, 4);
+    invoke.mockResolvedValue(bundle.buffer);
+    return { fonts: await import("./fonts"), invoke, registered, load, canvases };
+  }
+
+  it("loads an unavailable family once across primary, fallback and UI, including regular/bold/italic", async () => {
+    const { fonts, invoke, registered, load } = await resolver(false);
+    const family = fonts.monoFontFamily("JetBrainsMono Nerd Font Mono");
+    expect(family).toContain('"OpenIDEA User Font 0", "JetBrainsMono Nerd Font Mono"');
+    fonts.uiFontFamily("jetbrainsmono nerd font mono");
+    fonts.monoFontFamily("Inter", "JetBrainsMono Nerd Font Mono");
+    await fonts.fontsLoaded(family, 14);
+    expect(invoke).toHaveBeenCalledExactlyOnceWith("user_font_data", { family: "JetBrainsMono Nerd Font Mono" });
+    expect(registered.map((f) => f.descriptors)).toEqual([
+      { weight: "400", style: "normal" },
+      { weight: "700", style: "normal" },
+      { weight: "400", style: "italic" },
+    ]);
+    expect(load).toHaveBeenCalledTimes(2);
+  });
+
+  it("uses available local/system families without reading font data", async () => {
+    const { fonts, invoke } = await resolver(true);
+    expect(fonts.uiFontFamily("Menlo")).toBe('"Menlo", system-ui, sans-serif');
+    fonts.monoFontFamily("Maple Mono NF CN");
+    expect(invoke).not.toHaveBeenCalled();
+  });
+
+  it("loads a UI fallback through the shared macOS user font resolver", async () => {
+    const { fonts, invoke, registered } = await resolver(false);
+    const family = fonts.uiFontFamily("Inter", "Maple Mono NF CN");
+    expect(family).toBe('"Inter Variable", "Inter", "OpenIDEA User Font 0", "Maple Mono NF CN", system-ui, sans-serif');
+    expect(fonts.monoFontFamily("Inter", "Maple Mono NF CN")).toContain('"OpenIDEA User Font 0"');
+    await fonts.fontsLoaded(family, 13);
+    expect(invoke).toHaveBeenCalledExactlyOnceWith("user_font_data", { family: "Maple Mono NF CN" });
+    expect(registered).toHaveLength(3);
+  });
+
+  it("detects user fonts that WKWebView exposes only to connected canvases without loading bytes", async () => {
+    const { fonts, invoke, canvases } = await resolver("connected");
+    expect(fonts.fontAvailable("Maple Mono NF CN")).toBe(true);
+    expect(fonts.familyFaces("Maple Mono NF CN")).toEqual(['"Maple Mono NF CN"']);
+    expect(fonts.familyFaces("JetBrainsMono Nerd Font Mono")).toEqual(['"JetBrainsMono Nerd Font Mono"']);
+    expect(invoke).not.toHaveBeenCalled();
+    expect(canvases.length).toBeGreaterThan(0);
+    expect(canvases.every((canvas) => canvas.hidden && !canvas.isConnected)).toBe(true);
+  });
+
+  it("removes the probe when a font is unavailable or canvas measurement fails", async () => {
+    const { fonts, canvases } = await resolver(false);
+    expect(fonts.fontAvailable("Unavailable")).toBe(false);
+    expect(canvases.every((canvas) => !canvas.isConnected)).toBe(true);
+    const remove = vi.spyOn(HTMLCanvasElement.prototype, "remove");
+    vi.spyOn(HTMLCanvasElement.prototype, "getContext").mockImplementation(() => {
+      throw new Error("Canvas unavailable");
+    });
+    expect(fonts.fontAvailable("Maple Mono NF CN")).toBe(true);
+    expect(remove).toHaveBeenCalledOnce();
+  });
+
+  it("does not read a locally available symbol-only Nerd fallback", async () => {
+    const { fonts, invoke } = await resolver("symbols");
+    expect(fonts.familyFaces("Symbols Nerd Font Mono")).toEqual(['"Symbols Nerd Font Mono"']);
+    expect(invoke).not.toHaveBeenCalled();
+  });
+
+  it("never reads bundled webfonts even before their CSS faces load", async () => {
+    const { fonts, invoke } = await resolver(false);
+    fonts.monoFontFamily("Inter");
+    fonts.monoFontFamily("JetBrains Mono");
+    fonts.uiFontFamily("Inter Variable");
+    fonts.monoFontFamily("JetBrains Mono Variable");
+    expect(invoke).not.toHaveBeenCalled();
+  });
+
+  it("does not read bundled faces or alter other platforms", async () => {
+    const { fonts, invoke } = await resolver(false, "windows");
+    fonts.monoFontFamily("Inter");
+    fonts.monoFontFamily("JetBrains Mono");
+    expect(fonts.uiFontFamily("User Font")).toBe('"User Font", system-ui, sans-serif');
+    expect(invoke).not.toHaveBeenCalled();
   });
 });
diff --git a/src/platform/fonts.ts b/src/platform/fonts.ts
index dc0b7cd74..9acf9eb31 100644
--- a/src/platform/fonts.ts
+++ b/src/platform/fonts.ts
@@ -1,3 +1,6 @@
+import { invoke, isTauri } from "@tauri-apps/api/core";
+import { guessOs } from "./platformInfo";
+
 /**
  * Monospace font-family lists shared by every consumer of the editor / terminal
  * font. "JetBrains Mono" is the bundled default, but the bundle registers it as
@@ -10,6 +13,8 @@ export const BUNDLED_MONO_FAMILY = "JetBrains Mono";
 export const BUNDLED_UI_FAMILY = "Inter";
 const BUNDLED_FACES: ReadonlyMap<string, readonly string[]> = new Map([
   [BUNDLED_MONO_FAMILY.toLowerCase(), ['"JetBrains Mono Variable"', '"JetBrains Mono"']],
+  ["jetbrains mono variable", ['"JetBrains Mono Variable"']],
+  ["inter variable", ['"Inter Variable"']],
   [BUNDLED_UI_FAMILY.toLowerCase(), ['"Inter Variable"', '"Inter"']],
 ]);
 const MONO_STACK_FALLBACK = '"JetBrains Mono Variable", "JetBrains Mono", ui-monospace, Menlo, monospace';
@@ -22,10 +27,83 @@ export const quoteFontFamily = (family: string) =>
 // Preserve compatibility with previously saved names wrapped in CSS quotes.
 const familyName = (family: string) => family.trim().replace(/^"(.*)"$/, "$1");
 
+// Per webview: the CSS alias stays stable while its faces load; DOM consumers
+// reflow automatically and canvas consumers await the same promise below.
+const userFonts = new Map<string, { alias: string; loaded: Promise<void> }>();
+
+/** WKWebView needs a connected canvas to resolve user fonts. Remove it in finally after probing. */
+export function createFontProbeCanvas(): HTMLCanvasElement {
+  const canvas = document.createElement("canvas");
+  canvas.hidden = true;
+  (document.body ?? document.documentElement).append(canvas);
+  return canvas;
+}
+
+/** A pure local-name probe; FontFaceSet.check also returns true for unknown families. */
+export function fontAvailable(name: string): boolean {
+  let canvas: HTMLCanvasElement | undefined;
+  try {
+    canvas = createFontProbeCanvas();
+    const ctx = canvas.getContext("2d");
+    if (!ctx) return true;
+    // Symbol-only Nerd fonts and CJK faces may have no Latin glyphs.
+    return ["mmmmmmmmmmlli1WQ@", "\uF418\uE725\u{F0001}", "汉字かな한글"].some((sample) =>
+      ["monospace", "serif", "sans-serif"].some((base) => {
+        ctx.font = `32px ${base}`;
+        const baseline = ctx.measureText(sample).width;
+        ctx.font = `32px ${quoteFontFamily(name)}, ${base}`;
+        const width = ctx.measureText(sample).width;
+        return Number.isFinite(width) && Number.isFinite(baseline) && width !== baseline;
+      }),
+    );
+  } catch {
+    return true;
+  } finally {
+    canvas?.remove();
+  }
+}
+
+async function loadUserFont(name: string, alias: string): Promise<void> {
+  const buffer = await invoke<ArrayBuffer>("user_font_data", { family: name });
+  const headerLength = new DataView(buffer).getUint32(0, true);
+  const start = 4 + headerLength;
+  const faces: { weight: number; style: string; offset: number; length: number }[] = JSON.parse(
+    new TextDecoder().decode(buffer.slice(4, start)),
+  );
+  await Promise.all(
+    faces.map(async ({ weight, style, offset, length }) => {
+      const face = new FontFace(alias, buffer.slice(start + offset, start + offset + length), {
+        weight: String(weight),
+        style,
+      });
+      document.fonts.add(face);
+      try {
+        await face.load();
+      } catch {
+        document.fonts.delete(face);
+      }
+    }),
+  );
+}
+
 /** One resolver for primary, fallback and UI families, matching the bundled CSS registrations. */
-function familyFaces(family: string): readonly string[] {
+export function familyFaces(family: string): readonly string[] {
   const name = familyName(family);
-  return BUNDLED_FACES.get(name.toLowerCase()) ?? [quoteFontFamily(name)];
+  const bundled = BUNDLED_FACES.get(name.toLowerCase());
+  if (bundled) return bundled;
+  if (!name || !isTauri() || guessOs() !== "macos" || typeof FontFace === "undefined") return [quoteFontFamily(name)];
+  const key = name.toLowerCase();
+  let entry = userFonts.get(key);
+  if (!entry) {
+    if (fontAvailable(name)) return [quoteFontFamily(name)];
+    const alias = `OpenIDEA User Font ${userFonts.size}`;
+    const loaded = loadUserFont(name, alias).catch(() => {
+      /* retain local-name and bundled fallbacks */
+    });
+    entry = { alias, loaded };
+    userFonts.set(key, entry);
+  }
+  return [quoteFontFamily(entry.alias), quoteFontFamily(name)];
 }
 
 /** The `--font-mono` stack, resolved (canvas / xterm can't use `var()`). */
@@ -53,6 +131,8 @@ export function monoFontFamily(family: string | undefined, fallback = "", base =
 export async function fontsLoaded(family: string, size: number): Promise<void> {
   const fonts = typeof document !== "undefined" ? document.fonts : undefined;
   if (!fonts?.load) return;
+  const pending = [...userFonts.values()].filter(({ alias }) => family.includes(quoteFontFamily(alias)));
+  if (pending.length) await Promise.all(pending.map(({ loaded }) => loaded));
   try {
     await Promise.all([fonts.load(`${size}px ${family}`), fonts.load(`bold ${size}px ${family}`)]);
   } catch {
@@ -60,7 +140,8 @@ export async function fontsLoaded(family: string, size: number): Promise<void> {
   }
 }
 
-/** Bundled aliases also apply when selected for the interface. */
-export function uiFontFamily(family: string): string {
-  return [...familyFaces(family), "system-ui", "sans-serif"].join(", ");
+/** Bundled aliases also apply when selected for the interface; `fallback` covers glyphs `family` lacks (empty = none). */
+export function uiFontFamily(family: string, fallback = ""): string {
+  const fb = familyName(fallback);
+  return [...familyFaces(family), ...(fb ? familyFaces(fb) : []), "system-ui", "sans-serif"].join(", ");
 }
diff --git a/src/platform/ipc.ts b/src/platform/ipc.ts
index 9936911de..2fd06e815 100644
--- a/src/platform/ipc.ts
+++ b/src/platform/ipc.ts
@@ -14,10 +14,12 @@ export type * from "@/bindings";
 
 export class IpcError extends Error {
   readonly kind: IdeError["kind"];
+  readonly data: IdeError["data"];
   constructor(error: IdeError) {
     super(error.message);
     this.name = "IpcError";
     this.kind = error.kind;
+    this.data = error.data;
   }
 }
 
@@ -46,6 +48,11 @@ export function unavailableText(e: unknown, fallback = "No language server avail
   return e instanceof IpcError && e.kind === "unavailable" && LACKS_FEATURE.test(e.message) ? e.message : fallback;
 }
 
+/** True when `unavailable` means no server is running for the file, rather than a running server lacking the feature. */
+export function isNoServer(e: unknown): boolean {
+  return e instanceof IpcError && e.kind === "unavailable" && !LACKS_FEATURE.test(e.message);
+}
+
 // Ids are shared by every window of the backend and outlive a reload there (a cancel that
 // arrives before its request began is remembered), so each page starts at a random point.
 let nextId = 1 + Math.floor(Math.random() * 0x7000_0000);
diff --git a/src/platform/languageSettings.ts b/src/platform/languageSettings.ts
index ca4aa81eb..055ff9d47 100644
--- a/src/platform/languageSettings.ts
+++ b/src/platform/languageSettings.ts
@@ -42,6 +42,7 @@ export interface LanguagesValid {
     modules: { env: Record<string, string>; autoVendor: boolean };
   };
   typescript: { version: string };
+  prettier: { path: string; languages: string[]; prefer: boolean; runOnSave: boolean };
   java: {
     jdk: string;
     jdtlsJdk: string;
@@ -80,6 +81,27 @@ export const DEFAULT_LANGUAGES: LanguagesValid = {
   rust: { toolchain: "", stdlib: "", checkOnSave: true, checkCommand: "check", rustfmtArgs: "" },
   go: { goroot: "", gopath: "", buildTags: DEFAULT_GO_BUILD_TAGS, modules: { env: {}, autoVendor: true } },
   typescript: { version: "bundled" },
+  prettier: {
+    path: "",
+    languages: [
+      "markdown",
+      "yaml",
+      "css",
+      "scss",
+      "less",
+      "html",
+      "graphql",
+      "javascript",
+      "javascriptreact",
+      "typescript",
+      "typescriptreact",
+      "json",
+      "jsonc",
+      "vue",
+    ],
+    prefer: false,
+    runOnSave: false,
+  },
   java: {
     jdk: "",
     jdtlsJdk: "",
@@ -142,6 +164,7 @@ export function validateLanguages(raw: unknown): LanguagesValid {
   const tags = obj(go.buildTags);
   const modules = obj(go.modules);
   const ts = obj(l.typescript);
+  const prettier = obj(l.prettier);
   const java = obj(l.java);
   const maven = obj(java.maven);
   const gradle = obj(java.gradle);
@@ -177,6 +200,14 @@ export function validateLanguages(raw: unknown): LanguagesValid {
       },
     },
     typescript: { version: text(ts.version, d.typescript.version) || d.typescript.version },
+    prettier: {
+      path: text(prettier.path, d.prettier.path),
+      languages: Array.isArray(prettier.languages)
+        ? [...new Set(prettier.languages.filter((v): v is string => typeof v === "string"))]
+        : d.prettier.languages,
+      prefer: bool(prettier.prefer, d.prettier.prefer),
+      runOnSave: bool(prettier.runOnSave, d.prettier.runOnSave),
+    },
     java: {
       jdk: text(java.jdk, d.java.jdk),
       jdtlsJdk: text(java.jdtlsJdk, d.java.jdtlsJdk),
diff --git a/src/platform/locales/text/zh.json b/src/platform/locales/text/zh.json
index daff493a2..47c0c4be9 100644
--- a/src/platform/locales/text/zh.json
+++ b/src/platform/locales/text/zh.json
@@ -1,4 +1,8 @@
 {
+  "Kotlin bridge requires a Maven build root": "Kotlin 桥接需要 Maven 构建根目录",
+  "Kotlin bridge bundle is unavailable": "Kotlin 桥接扩展不可用",
+  "Kotlin bridge command did not acknowledge its library snapshot": "Kotlin 桥接命令未确认类库更新",
+  "Kotlin editor compilation failed": "Kotlin 编辑器编译失败",
   "Updating results…": "正在更新结果…",
   "Uploading files": "正在上传文件",
   "No files on the clipboard": "剪贴板中没有文件",
@@ -760,6 +764,7 @@
   "Failed": "失败",
   "Failed to restart language server": "重启语言服务器失败",
   "Fallback font": "备用字体",
+  "Fallback font:": "备用字体：",
   "Fetch": "获取",
   "Fetches remotes in the background so incoming commits show in the Branches popup. Auto stops after an authentication failure.": "在后台获取远程，以便传入的提交显示在“分支”弹出窗口中。“自动”在身份验证失败后停止。",
   "Field access": "字段访问",
@@ -1595,6 +1600,27 @@
   "Refactor This…": "重构此项…",
   "Refactoring undone": "重构已撤消",
   "Reformat Code": "重新格式化代码",
+  "Prettier path": "Prettier 路径",
+  "Auto: nearest project node_modules, managed installation, then PATH. An explicit path overrides auto detection.": "自动：依次查找最近的项目 node_modules、受管安装和 PATH。指定路径将覆盖自动检测。",
+  "Formatting provider": "格式化工具",
+  "Automatic (language server first)": "自动（优先语言服务器）",
+  "Run on save": "保存时运行",
+  "Run Prettier on save for enabled languages when it is the selected formatting provider.": "对已启用的语言，在选择 Prettier 作为格式化工具时于保存时运行。",
+  "Enabled languages": "启用的语言",
+  "Reformat Code needs {name}. Install it via {method}?": "重新格式化代码需要 {name}。是否通过 {method} 安装？",
+  "Install Missing Tool": "安装缺失的工具",
+  "Prettier formatting failed": "Prettier 格式化失败",
+  "Prettier formatting timed out": "Prettier 格式化超时",
+  "Prettier does not support selection formatting for this language; formatted the whole file": "Prettier 不支持此语言的选区格式化，已格式化整个文件",
+  "Formatting timed out": "格式化超时",
+  "Prettier: Node.js is required": "Prettier：需要 Node.js",
+  "Formatter": "格式化工具",
+  "JSON with Comments": "带注释的 JSON",
+  "Unknown external formatter: {tool}": "未知的外部格式化工具：{tool}",
+  "Prettier: package has no CLI entry point": "Prettier：软件包未提供命令行入口",
+  "Prettier: CLI does not exist: {path}": "Prettier：命令行程序不存在：{path}",
+  "Prettier: file has no directory": "Prettier：文件路径不含目录",
+  "Prettier: {error}": "Prettier：{error}",
   "Reformat File": "重新格式化文件",
   "Reformat code": "重新格式化代码",
   "Reformat code on save": "保存时重新格式化代码",
@@ -1985,6 +2011,8 @@
   "Show the parameter info popup in": "在以下时间后显示形参信息弹出窗口",
   "Show the selected coverage suite in editors and the project view": "在编辑器和项目视图中显示所选覆盖率套件",
   "Show tool window bars": "显示工具窗口栏",
+  "Show tool window badges": "显示工具窗口角标",
+  "Counts on the stripe icons, e.g. changed files or agent tasks needing input": "侧栏图标上的数字，如变更文件数、等待输入的智能体任务数",
   "Show tool window names": "显示工具窗口名称",
   "Show value tooltip on code selection": "选中代码时显示值提示",
   "Show value tooltip on mouse hover": "鼠标悬停时显示值工具提示",
@@ -2221,6 +2249,7 @@
   "Merged with main toolbar": "与主工具栏合并",
   "UI Options": "UI 选项",
   "UI elements take up less screen space": "UI 元素占用更少的屏幕空间",
+  "UI fallback font": "UI 备用字体",
   "UI font": "UI 字体",
   "UI font size": "UI 字体大小",
   "Uninstalled {name}": "已卸载 {name}",
@@ -4465,6 +4494,7 @@
   "Plan node properties": "计划节点属性",
   "Values": "值",
   "Vim rc file": "Vim rc 文件",
+  "Breakpoints are not supported in output classes without source code.": "输出目录中无源码的类不支持断点。",
   "Decompiled .class file: sources are not available.": "已反编译的 .class 文件：没有可用的源代码。",
   "No column of the file matches the table": "文件中没有与该表匹配的列",
   "Not a URL of PostgreSQL, MySQL, SQLite or a compatible database": "不是 PostgreSQL、MySQL、SQLite 或兼容数据库的 URL",
@@ -5379,5 +5409,36 @@
   "in {length} repositories": "在 {length} 个仓库中",
   "No repository in the selection has revision {label}": "所选内容中的仓库均无版本 {label}",
   "{repoName} has no revision {label}": "{repoName} 没有版本 {label}",
-  "Waiting for language server…": "正在等待语言服务器…"
+  "Waiting for language server…": "正在等待语言服务器…",
+  "Compare Directories": "比较目录",
+  "Select two directories to compare": "选择两个要比较的目录",
+  "Select a directory to compare": "选择要比较的目录",
+  "Directory path": "目录路径",
+  "Only on left": "仅左侧",
+  "Only on right": "仅右侧",
+  "Contents differ": "内容不同",
+  "Comparing directories": "正在比较目录",
+  "Filter by name": "按名称过滤",
+  "Show identical files": "显示相同文件",
+  "Copy to Left": "复制到左侧",
+  "Copy to Right": "复制到右侧",
+  "Compared files": "比较的文件",
+  "Comparison cancelled": "已取消比较",
+  "No matching differences": "没有匹配的差异",
+  "Overwrite files?": "覆盖文件？",
+  "Copy to {to} and overwrite existing files?": "复制到 {to} 并覆盖已有文件？",
+  "Left: {left}": "左侧：{left}",
+  "Right: {right}": "右侧：{right}",
+  "Compared {compared} of {total} entries": "已比较 {compared} / {total} 个条目",
+  "Scanned {scanned} entries": "已扫描 {scanned} 个条目",
+  "Binary content": "二进制内容",
+  "Binary files cannot be shown as text": "二进制文件无法以文本形式显示",
+  "Delete {path}?": "删除 {path}？",
+  "copy requires an absolute path": "复制需要绝对路径",
+  "missing file name": "缺少文件名",
+  "copy requires absolute paths": "复制需要绝对路径",
+  "copy paths must belong to the comparison roots": "复制路径必须位于比较的根目录内",
+  "cannot copy overlapping paths": "无法在相互包含的路径之间复制",
+  "cannot copy through a destination symlink": "无法通过目标目录内的符号链接复制",
+  "expected a relative comparison entry path": "需要比较条目的相对路径"
 }
diff --git a/src/platform/locales/textCatalog.test.ts b/src/platform/locales/textCatalog.test.ts
index b0963067f..86841e022 100644
--- a/src/platform/locales/textCatalog.test.ts
+++ b/src/platform/locales/textCatalog.test.ts
@@ -79,6 +79,8 @@ const BUILT_AT_RUNTIME = new Set<string>([]);
 
 /** Text that stays as written in every locale: names, code, formats, shortcuts. */
 const UNTRANSLATED = new Set<string>([
+  // Product names
+  "Prettier",
   // Go environment variables and placeholder values
   "CGO",
   "GOPROXY",
diff --git a/src/platform/virtualDocs.ts b/src/platform/virtualDocs.ts
index 8a31ef0ef..f0ced78e8 100644
--- a/src/platform/virtualDocs.ts
+++ b/src/platform/virtualDocs.ts
@@ -4,12 +4,13 @@
  * code). Locations into them carry the URI as their `path`; the editor opens
  * them as `virtual` editor inputs instead of files.
  */
+import { isClassFile } from "./classFiles";
 import { call, commands, type VirtualDocument } from "./ipc";
 
-/** True for `scheme:…` URIs other than `file:` (scheme of 2+ chars, so `C:\…` is a path). */
+/** Server document URIs, including decompiled disk classes; drive letters remain paths. */
 export function isVirtualUri(s: string | null | undefined): boolean {
   const m = /^([a-zA-Z][a-zA-Z0-9+.-]+):/.exec(s ?? "");
-  return !!m && m[1]!.toLowerCase() !== "file";
+  return !!m && (m[1]!.toLowerCase() !== "file" || isClassFile(s!));
 }
 
 /** Last path segment of a URI (without query / fragment), e.g. `SpringApplication.class`. */
diff --git a/src/ui/List.tsx b/src/ui/List.tsx
index 5a361ddcd..71417a26d 100644
--- a/src/ui/List.tsx
+++ b/src/ui/List.tsx
@@ -16,6 +16,7 @@ import {
 } from "react";
 import clsx from "clsx";
 import { useVirtualizer } from "@tanstack/react-virtual";
+import { rowSelectionMode } from "./rowSelection";
 import styles from "./List.module.css";
 
 export interface ListRowState {
@@ -32,6 +33,8 @@ export interface ListProps<T> {
   activeIndex?: number;
   defaultActiveIndex?: number;
   onActiveChange?: (index: number) => void;
+  /** Opt into modifier selection; modified clicks select without activating. */
+  onSelect?: (index: number, e: KeyboardEvent | MouseEvent) => void;
   /** Rows selected besides the active one (multi-selection); drawn like the active row. */
   isSelected?: (item: T, index: number) => boolean;
   onActivate?: (item: T, index: number, e: KeyboardEvent | MouseEvent) => void;
@@ -115,6 +118,7 @@ export function List<T>({
   activeIndex,
   defaultActiveIndex,
   onActiveChange,
+  onSelect,
   isSelected,
   onActivate,
   onContextMenu,
@@ -169,7 +173,8 @@ export function List<T>({
     const next = listNavigate(e.key, { items, active, isSection, pageSize });
     if (next === null) return;
     e.preventDefault();
-    if (next !== active) setActive(next);
+    if (onSelect) onSelect(next, e);
+    else if (next !== active) setActive(next);
   };
 
   if (!items.length && empty) return <div className={clsx(styles.list, styles.emptyWrap, className)}>{empty}</div>;
@@ -178,6 +183,7 @@ export function List<T>({
     <div
       ref={scrollRef}
       role="listbox"
+      aria-multiselectable={onSelect ? true : undefined}
       aria-label={aria["aria-label"]}
       aria-labelledby={aria["aria-labelledby"]}
       aria-activedescendant={
@@ -209,6 +215,7 @@ export function List<T>({
               id={`${baseId}-${v.index}`}
               role="option"
               aria-selected={selected}
+              data-lead={isActive || undefined}
               aria-posinset={optionIndex.idx[v.index]}
               aria-setsize={optionIndex.count}
               className={clsx(styles.row, selected && styles.active)}
@@ -217,9 +224,12 @@ export function List<T>({
               onMouseDown={(e) => {
                 if (e.button !== 0) return;
                 if (!focusable) e.preventDefault();
-                setActive(v.index);
+                if (!onSelect) setActive(v.index);
+              }}
+              onClick={(e) => {
+                onSelect?.(v.index, e);
+                if (!onSelect || rowSelectionMode(e) === "single") onActivate?.(item, v.index, e);
               }}
-              onClick={(e) => onActivate?.(item, v.index, e)}
               onContextMenu={onContextMenu ? (e) => onContextMenu(item, v.index, e) : undefined}
             >
               {renderItem(item, { active: isActive, index: v.index })}
diff --git a/src/ui/index.ts b/src/ui/index.ts
index 21427a32f..669975184 100644
--- a/src/ui/index.ts
+++ b/src/ui/index.ts
@@ -33,3 +33,4 @@ export { lazyComponent, prefetchLazyComponents } from "./lazy";
 export { T } from "./T";
 export { selectableText, copyMenuFor, copyText } from "./selectableText";
 export { useSelectionBoundary } from "./useSelectionBoundary";
+export * from "./rowSelection";
diff --git a/src/ui/rowSelection.test.ts b/src/ui/rowSelection.test.ts
new file mode 100644
index 000000000..c06936aec
--- /dev/null
+++ b/src/ui/rowSelection.test.ts
@@ -0,0 +1,22 @@
+import { describe, expect, it } from "vitest";
+import { selectRow, selectedRows } from "./rowSelection";
+
+describe("list selection across sections", () => {
+  it("selects only options across headers in either direction", () => {
+    const rows = [
+      { key: "files", section: true },
+      { key: "a", section: false },
+      { key: "symbols", section: true },
+      { key: "b", section: false },
+      { key: "actions", section: true },
+      { key: "c", section: false },
+    ];
+    const single = { lead: 3, anchor: 3, keys: null };
+    const section = (row: (typeof rows)[number]) => row.section;
+    const down = selectRow(rows, single, 5, "range", section);
+    expect(selectedRows(rows, down).map((r) => r.key)).toEqual(["b", "c"]);
+    const up = selectRow(rows, down, 1, "range", section);
+    expect(selectedRows(rows, up).map((r) => r.key)).toEqual(["a", "b"]);
+    expect(selectRow(rows, up, 2, "toggle", section)).toBe(up);
+  });
+});
diff --git a/src/ui/rowSelection.ts b/src/ui/rowSelection.ts
new file mode 100644
index 000000000..05c8261dc
--- /dev/null
+++ b/src/ui/rowSelection.ts
@@ -0,0 +1,74 @@
+import { hasPrimaryModifier } from "@/platform/keymap";
+
+/**
+ * Multi-selection of list rows: click / ↑↓ select one row,
+ * ⇧ extends from the anchor, ⌘/Ctrl toggles a row.
+ */
+
+export interface RowSelection {
+  /** Active row (keyboard focus, preview). */
+  lead: number;
+  /** Start of ⇧ ranges. */
+  anchor: number;
+  /** Keys of the selected rows; `null` when only the lead is selected. */
+  keys: ReadonlySet<string> | null;
+}
+
+export const SINGLE_FIRST: RowSelection = { lead: 0, anchor: 0, keys: null };
+
+export function selectRow<T extends { key: string }>(
+  rows: readonly T[],
+  sel: RowSelection,
+  index: number,
+  mode: "single" | "range" | "toggle" = "single",
+  isSection?: (row: T) => boolean,
+): RowSelection {
+  if (index < 0 || index >= rows.length || isSection?.(rows[index]!)) return sel;
+  if (mode === "range") {
+    const anchor = Math.min(Math.max(0, sel.anchor), rows.length - 1);
+    const [a, b] = anchor <= index ? [anchor, index] : [index, anchor];
+    return {
+      lead: index,
+      anchor,
+      keys: new Set(
+        rows
+          .slice(a, b + 1)
+          .filter((r) => !isSection?.(r))
+          .map((r) => r.key),
+      ),
+    };
+  }
+  if (mode === "toggle") {
+    const keys = new Set(sel.keys ?? (rows[sel.lead] ? [rows[sel.lead]!.key] : []));
+    const key = rows[index]!.key;
+    if (!keys.has(key)) return { lead: index, anchor: index, keys: keys.add(key) };
+    keys.delete(key);
+    const rest = rows.findLastIndex((r) => keys.has(r.key));
+    if (rest < 0) return { lead: index, anchor: index, keys: null };
+    return { lead: rest, anchor: rest, keys };
+  }
+  return { lead: index, anchor: index, keys: null };
+}
+
+/** The selected rows in list order (the lead when nothing else is selected). */
+export function selectedRows<T extends { key: string }>(rows: readonly T[], sel: RowSelection): T[] {
+  if (!rows.length || sel.lead < 0) return [];
+  const lead = Math.min(sel.lead, rows.length - 1);
+  if (!sel.keys) return [rows[lead]!];
+  const out = rows.filter((r) => sel.keys!.has(r.key));
+  return out.length ? out : [rows[lead]!];
+}
+
+export function isRowSelected(sel: RowSelection, key: string): boolean {
+  return !!sel.keys?.has(key);
+}
+
+export function rowSelectionMode(e?: {
+  shiftKey: boolean;
+  metaKey: boolean;
+  ctrlKey: boolean;
+  type: string;
+}): "single" | "range" | "toggle" {
+  if (e?.shiftKey) return "range";
+  return e?.type === "click" && hasPrimaryModifier(e) ? "toggle" : "single";
+}
diff --git a/src/workbench/Workbench.test.tsx b/src/workbench/Workbench.test.tsx
index 67ff74783..f8f8f7175 100644
--- a/src/workbench/Workbench.test.tsx
+++ b/src/workbench/Workbench.test.tsx
@@ -148,6 +148,17 @@ describe("notifications", () => {
     expect(useNotifications.getState().items).toHaveLength(2);
   });
 
+  it("explicitly non-sticky errors fade after the ordinary balloon timeout", () => {
+    vi.useFakeTimers();
+    vi.spyOn(document, "hasFocus").mockReturnValue(true);
+    render(<Balloons />);
+    act(() => void notify({ level: "error", title: "Formatting failed", sticky: false }));
+    expect(screen.getByRole("alert")).toHaveTextContent("Formatting failed");
+    act(() => vi.advanceTimersByTime(BALLOON_TIMEOUT.info! + 10));
+    expect(screen.queryByText("Formatting failed")).toBeNull();
+    expect(useNotifications.getState().items[0]).toMatchObject({ sticky: false, balloon: false });
+  });
+
   it("sticky balloons fade into the tool window after 5 minutes, staying unread", () => {
     vi.useFakeTimers();
     vi.spyOn(document, "hasFocus").mockReturnValue(true);
diff --git a/src/workbench/notificationStore.ts b/src/workbench/notificationStore.ts
index f67a384f5..5069884a5 100644
--- a/src/workbench/notificationStore.ts
+++ b/src/workbench/notificationStore.ts
@@ -2,6 +2,7 @@
 import type { ReactNode } from "react";
 import { create } from "zustand";
 import { call, commands, onIdeEvent } from "@/platform/ipc";
+import { tx } from "@/platform/i18n";
 import { useProject } from "@/platform/project";
 import type { NotificationService } from "./contributions";
 
@@ -116,8 +117,8 @@ export const STICKY_BALLOON_TIMEOUT = 5 * 60 * 1000;
 
 /** Fade-out delay of a balloon, or null when it stays until dismissed. */
 export function balloonTimeout(n: Pick<IdeNotification, "level" | "sticky" | "logged">): number | null {
-  if (n.sticky || BALLOON_TIMEOUT[n.level] === null) return n.logged ? STICKY_BALLOON_TIMEOUT : null;
-  return BALLOON_TIMEOUT[n.level];
+  if (n.sticky) return n.logged ? STICKY_BALLOON_TIMEOUT : null;
+  return BALLOON_TIMEOUT[n.level] ?? BALLOON_TIMEOUT.info;
 }
 const MAX_HISTORY = 200;
 let seq = 0;
@@ -189,5 +190,8 @@ export const notificationServiceImpl: NotificationService = {
 };
 
 export function installNotifyEvents(): () => void {
-  return onIdeEvent("notify", (e) => void notify({ level: e.level, title: e.title, body: e.body ?? undefined }));
+  return onIdeEvent(
+    "notify",
+    (e) => void notify({ level: e.level, title: tx(e.title), body: e.body ? tx(e.body) : undefined }),
+  );
 }
diff --git a/src/workbench/toolwindows/ToolWindows.tsx b/src/workbench/toolwindows/ToolWindows.tsx
index 3d874c903..d957e2a7d 100644
--- a/src/workbench/toolwindows/ToolWindows.tsx
+++ b/src/workbench/toolwindows/ToolWindows.tsx
@@ -359,8 +359,10 @@ function startStripeDrag(e: PointerEvent<HTMLButtonElement>, id: string) {
 }
 
 function StripeBadge({ useBadge }: { useBadge: () => number | string | null }) {
+  // Settings › Appearance › Tool Windows › "Show tool window badges".
+  const showBadges = useProject((s) => s.settings?.appearance?.showToolWindowBadges) !== false;
   const value = useBadge();
-  if (value === null || value === 0 || value === "") return null;
+  if (!showBadges || value === null || value === 0 || value === "") return null;
   return <span className={styles.badge}>{typeof value === "number" && value > 99 ? "99+" : value}</span>;
 }
 
diff --git a/src/workbench/toolwindows/badges.test.tsx b/src/workbench/toolwindows/badges.test.tsx
new file mode 100644
index 000000000..1a6741e63
--- /dev/null
+++ b/src/workbench/toolwindows/badges.test.tsx
@@ -0,0 +1,43 @@
+import { act, render, screen } from "@testing-library/react";
+import { afterEach, beforeEach, expect, it } from "vitest";
+import { create } from "zustand";
+import { useProject } from "@/platform/project";
+import { ToolWindowStripe } from "./ToolWindows";
+import { resetToolWindowLayout, useToolWindowLayout } from "./store";
+
+beforeEach(() => {
+  resetToolWindowLayout();
+  useProject.setState({ settings: null });
+});
+
+afterEach(() => useProject.setState({ settings: null }));
+
+it("hides stripe counts immediately and restores the current count when enabled", () => {
+  const useCount = create(() => ({ count: 3 }));
+  render(
+    <ToolWindowStripe
+      side="left"
+      visible={useToolWindowLayout.getState().visible}
+      windows={[
+        {
+          id: "git",
+          title: "Git",
+          icon: "folder",
+          anchor: "left",
+          component: () => null,
+          useBadge: () => useCount((s) => s.count),
+        },
+      ]}
+    />,
+  );
+  const button = screen.getByRole("button", { name: "Git" });
+  expect(button).toHaveTextContent("3");
+  act(() => useProject.setState({ settings: { appearance: { showToolWindowBadges: false } } }));
+  expect(button).not.toHaveTextContent("3");
+  act(() => useCount.setState({ count: 7 }));
+  expect(button).not.toHaveTextContent("7");
+  act(() => useProject.setState({ settings: { appearance: { showToolWindowBadges: true } } }));
+  expect(button).toHaveTextContent("7");
+  act(() => useCount.setState({ count: 0 }));
+  expect(button).not.toHaveTextContent("0");
+});