fix(plugins): list the marketplace and install plugins from the welcome screen

The Plugins page on the welcome screen showed "[object Object]" and "There
is no online plugin repository" (even with a marketplace configured), and
Install did nothing.

- Marketplace and package commands (index, download, unpack, install
  preview, theme import) only touch the IDE's own state and are allowed
  without a trusted project.
- Installing, uninstalling, enabling and granting plugins are allowed
  where no project is open; an untrusted project still blocks them.
- Errors rejected as plain backend error objects show their message, and
  a marketplace that couldn't be read shows the error instead of the
  "no online repository" note.

crates/ide-host/src/trust.rs

@@ -274,6 +274,15 @@ pub fn restricted_command_allowed(cmd: &str) -> bool {
             | "plugin_set_theme_frame"
             | "plugin_catalog"
             | "plugin_assets"
+            | "plugin_market"
+            | "plugin_market_url"
+            | "plugin_set_market_url"
+            | "plugin_market_download"
+            | "plugin_unpack_package"
+            | "plugin_stage_package"
+            | "plugin_preview_install"
+            | "plugin_read_intellij_theme"
+            | "plugin_installed_intellij_themes"
             | "notebook_open"
             | "notebook_get"
             | "notebook_edit"
@@ -319,12 +328,31 @@ pub fn restricted_command_allowed(cmd: &str) -> bool {
     ) || cmd.starts_with("plugin:")
 }
 
+/// Commands that change which plugin code runs: allowed where no project is open (the
+/// welcome screen), otherwise only in a trusted project.
+pub fn projectless_command_allowed(cmd: &str) -> bool {
+    matches!(
+        cmd,
+        "plugin_install_dir"
+            | "plugin_uninstall"
+            | "plugin_set_enabled"
+            | "plugin_grant"
+            | "plugin_set_capability"
+            | "plugin_roll_back"
+            | "plugin_reload"
+    )
+}
+
 impl crate::Host {
     pub fn authorize_command(&self, window: &str, command: &str) -> IdeResult<()> {
         if restricted_command_allowed(command) {
             return Ok(());
         }
-        self.project(window)?.require_trust()
+        match self.project(window) {
+            Ok(project) => project.require_trust(),
+            Err(_) if projectless_command_allowed(command) => Ok(()),
+            Err(error) => Err(error),
+        }
     }
 }
 

crates/ide-host/tests/trust.rs

@@ -58,6 +58,11 @@ async fn application_commands_work_in_restricted_projects_and_without_a_project(
         "vcs_write_patch",
         "remote_bootstrap_list",
         "deploy_test_connection",
+        "plugin_market",
+        "plugin_market_url",
+        "plugin_set_market_url",
+        "plugin_market_download",
+        "plugin_preview_install",
     ] {
         assert!(ide_host::trust::restricted_command_allowed(command), "{command}");
         for window in ["main", "welcome"] {
@@ -72,8 +77,6 @@ async fn application_commands_work_in_restricted_projects_and_without_a_project(
         "tools_list",
         "tools_install",
         "tools_uninstall",
-        "plugin_install_dir",
-        "plugin_reload",
         "vcs_git_version",
         "docker_compose_op",
         "db_execute",
@@ -93,6 +96,12 @@ async fn application_commands_work_in_restricted_projects_and_without_a_project(
             assert!(host.authorize_command(window, command).is_err(), "{window}: {command}");
         }
     }
+    // Plugin installs run plugin code: from the welcome screen, but not in an untrusted project.
+    for command in ["plugin_install_dir", "plugin_uninstall", "plugin_set_enabled", "plugin_reload"] {
+        assert!(!ide_host::trust::restricted_command_allowed(command), "{command}");
+        assert!(host.authorize_command("main", command).is_err(), "{command}");
+        assert!(host.authorize_command("welcome", command).is_ok(), "{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(