fix(vcs): handle repositories nested below a non-Git project root

- Project view: the Git submenu was gated on the project root being a
  repository, so it never appeared when the repositories are found later
  below a non-Git root. It now also follows the VCS availability that the
  Commit tool window uses.
- Commit: when only one repository had included changes, every staged but
  excluded file of every repository was passed to it, and the commit failed
  with "<path> is outside the repository". Paths that belong to another known
  repository are now left to that repository.

Fixes #2517
Fixes #2518

src/features/project-tree/contextMenu.test.ts

@@ -1,3 +1,4 @@
+import { clearContext, setContext } from "@/platform/context";
 import { afterEach, beforeEach, describe, expect, it } from "vitest";
 import { registerActions } from "@/platform/actions";
 import { useProject } from "@/platform/project";
@@ -88,6 +89,17 @@ describe("project view context menu", () => {
     expect(labels(contextMenuItems([node("/p/a.txt"), node("/p/b.txt")]))).toContain("Compare Files");
   });
 
+  it("offers Git for repositories found below a non-Git project root", () => {
+    useProject.setState({ project: { name: "p", root: ROOT, trusted: true, isGit: false, settings: {} } as never });
+    expect(sub(contextMenuItems([node("/p/a.py")]), "Git")).toBeUndefined();
+    setContext("vcsAvailable", true);
+    try {
+      expect(sub(contextMenuItems([node("/p/a.py")]), "Git")).toContain("Commit File…");
+    } finally {
+      clearContext("vcsAvailable");
+    }
+  });
+
   it("follows IDEA's order for a file", () => {
     const items = contextMenuItems([node(`${ROOT}/src/a.py`)]);
     expect(labels(items)).toEqual([

src/features/project-tree/contextMenu.ts

@@ -1,5 +1,6 @@
 /** Context menu and "New" popup of the project view. */
 import { executeAction, getAction } from "@/platform/actions";
+import { getContext } from "@/platform/context";
 import { canRevealInFileManager, fileManagerName } from "@/platform/fileManager";
 import { formatBinding, hostBinding, isMacHost, shortcutLabel } from "@/platform/keymap";
 import { relativePath, useProject } from "@/platform/project";
@@ -332,8 +333,8 @@ export function contextMenuItems(nodes: ProjectNode[]): MenuItem[] {
     { kind: "separator" },
   );
 
-  // Git ›
-  if (inProject && project?.isGit) {
+  // Git › (`vcsAvailable` also covers repositories nested below a non-Git project root)
+  if (inProject && (project?.isGit || getContext().vcsAvailable === true)) {
     const arg = vcsArg(nodes);
     const dirs = nodes.some((n) => n.dir);
     push(

src/features/vcs/__tests__/pluginCommit.test.ts

@@ -76,6 +76,23 @@ describe("the commit plugins see", () => {
     expect(draftRevision()).toBeGreaterThan(before);
   });
 
+  it("leaves another repository's staged files out of the only repository committed", async () => {
+    const staged: FileStatus = {
+      path: "/w/b/new.yml",
+      relPath: "new.yml",
+      staged: "added",
+      unstaged: null,
+      renamedFrom: null,
+    };
+    const changed: FileStatus = { ...files[0]!, path: "/w/a/Foo.java", relPath: "Foo.java" };
+    useVcs.setState({ root: "/w", repo: "/w/a", roots: ["/w/a", "/w/b"], status: [changed, staged] });
+    useCommit.setState({ checks: new Map([["/w/b/new.yml", "none" as const]]) });
+    const selection = (await maybeCommitService()!.selection())!;
+    expect(selection.repositories).toEqual([
+      { root: "/w/a", options: expect.objectContaining({ stage: ["/w/a/Foo.java"], exclude: [] }) },
+    ]);
+  });
+
   it("is null without a repository", async () => {
     useVcs.setState({ root: null });
     expect(await maybeCommitService()!.selection()).toBeNull();

src/features/vcs/commitSelection.ts

@@ -86,7 +86,11 @@ export async function selectionOf(plan: CommitPlan): Promise<CommitSelection> {
   const stage = [...plan.stage, ...partial.whole];
   const fallback = useVcs.getState().root ?? "";
   const repositories = repos.map((repo) => {
-    const inRepo = (path: string) => repos.length === 1 || (rootOf(path, roots) ?? null) === repo;
+    // A path in another known repository never goes to this one, even when it is the only one committed.
+    const inRepo = (path: string) => {
+      const root = rootOf(path, roots);
+      return root === null ? repos.length === 1 : root === repo;
+    };
     const options: CommitOptions = {
       amend,
       signOff,