fix(server): stop reporting a separate git dir as a branch's worktree

apps/server/src/vcs/GitVcsDriverCore.test.ts

@@ -694,6 +694,35 @@
   ).pipe(Effect.provide(ServerConfigLayer.pipe(Layer.provideMerge(NodeServices.layer)))),
 );
 
+it.effect("does not report a separate git dir as the worktree of its branch", () =>
+  Effect.scoped(
+    Effect.gen(function* () {
+      const driver = yield* makeGitVcsDriverCore();
+      const cwd = yield* makeTmpDir();
+      const gitDir = NodeFS.realpathSync(yield* makeTmpDir());
+      yield* git(cwd, ["init", `--separate-git-dir=${gitDir}`]).pipe(
+        Effect.provideService(GitVcsDriver.GitVcsDriver, driver),
+      );
+      yield* git(cwd, ["config", "user.email", "test@example.com"]).pipe(
+        Effect.provideService(GitVcsDriver.GitVcsDriver, driver),
+      );
+      yield* git(cwd, ["config", "user.name", "Test"]).pipe(
+        Effect.provideService(GitVcsDriver.GitVcsDriver, driver),
+      );
+      yield* git(cwd, ["commit", "--allow-empty", "-m", "init"]).pipe(
+        Effect.provideService(GitVcsDriver.GitVcsDriver, driver),
+      );
+      const refs = yield* driver.listRefs({ cwd, refresh: true });
+
+      assert.isTrue(refs.isRepo);
+      const current = refs.refs.find((ref) => ref.current);
+      assert.isDefined(current);
+      assert.notEqual(current?.worktreePath, gitDir);
+      assert.equal(current?.worktreePath, NodeFS.realpathSync(cwd));
+    }),
+  ).pipe(Effect.provide(ServerConfigLayer.pipe(Layer.provideMerge(NodeServices.layer)))),
+);
+
 it.effect("refreshes the current branch after an external checkout", () =>
   Effect.scoped(
     Effect.gen(function* () {
@@ -776,7 +805,7 @@
       yield* runGit(cwd, ["worktree", "add", "-b", "feature/linked", worktreePath]);
       yield* runGit(worktreePath, [
         "branch",
         "--set-upstream-to",
         `origin/${initialBranch}`,
         "feature/linked",
       ]);

apps/server/src/vcs/GitVcsDriverCore.ts

@@ -2829,9 +2829,13 @@ export const makeGitVcsDriverCore = Effect.fn("makeGitVcsDriverCore")(function*
               [branchName, path.normalize(path.resolve(worktreePath))] as const,
           )
         : [];
+    // With a separate git dir lacking `core.worktree`, git lists the git dir itself as the
+    // main worktree. It is not a checkout, so it must never be offered as one.
+    const normalizedGitCommonDir = path.normalize(path.resolve(gitCommonDir));
     const existingWorktreeEntries = yield* Effect.filter(
       parsedWorktreeEntries,
       ([, worktreePath]) =>
+        worktreePath !== normalizedGitCommonDir &&
         fileSystem.stat(worktreePath).pipe(
           Effect.as(true),
           Effect.orElseSucceed(() => false),
@@ -3026,6 +3030,13 @@ export const makeGitVcsDriverCore = Effect.fn("makeGitVcsDriverCore")(function*
         snapshot.localBranches.some((ref) => ref.worktreePath === repositoryPaths.worktreeRoot);
       const localBranches = snapshot.localBranches.map((ref) => ({
         ...ref,
+        // A separate git dir is filtered out of the worktree list, which leaves the
+        // current branch without a path; fall back to the folder the user opened.
+        worktreePath:
+          ref.worktreePath ??
+          (!ref.isRemote && ref.name === repositoryPaths.currentBranch
+            ? repositoryPaths.worktreeRoot
+            : null),
         current: hasCurrentWorktreeBranch
           ? ref.worktreePath === repositoryPaths.worktreeRoot
           : ref.name === repositoryPaths.currentBranch,