fix(server): keep separate Git metadata out of worktree paths

[a3ylf]

What Changed

Exclude the Git metadata directory from reusable worktree paths. Resolve the current branch's checkout from the caller's --show-toplevel result without storing that caller-specific path in the ref snapshot shared by linked worktrees.

Why

With --separate-git-dir, git worktree list can report the metadata directory as the main checkout. T3 accepted that existing directory and could reuse it for a thread, losing access to project files and local skills.

Fixes #12204.

Validation

• Both new real-Git regressions fail on main and pass with this change. They cover external metadata with and without core.worktree, a nested project directory, and a ref cache first populated by a linked worktree.
• 232 tests passed across GitVcsDriverCore, GitVcsDriver, and GitManager.
• Server typecheck and scoped formatting/lint passed; lint reports one existing inline-schema warning outside the change.
• Verified on Linux with Git 2.43.0. No desktop or mobile UI run.

Checklist

• This PR is small and focused
• I explained what changed and why
• UI screenshots and interaction video are not applicable to this server-only change

Model: GPT-6. Harness: Codex.

Summary by CodeRabbit

• Bug Fixes
  • Corrected worktree path reporting for repositories that use separate Git metadata directories.
  • Improved current-branch detection for main and linked worktrees, including access through nested directories.
  • Prevented Git metadata paths from being incorrectly treated as reusable worktree locations.

[macroscopeapp]

Approvability

Verdict: Approved at eff1bfe

Macroscope's review found this PR approvable — This small server-side fix prevents Git metadata directories from being reused as worktrees and keeps caller-specific checkout paths out of shared ref-cache data. The behavior is narrowly scoped and covered by targeted real-Git regression tests.

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[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

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Review profile: CHILL

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Run ID: 41181c4d-9701-494f-be05-74dcdface10b

📥 Commits

Reviewing files that changed from the base of the PR and between 4749035 and eff1bfe.

📒 Files selected for processing (2)

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

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📝 Walkthrough

Walkthrough

The Git VCS driver now excludes separate Git metadata directories from reusable worktrees and reports the caller’s worktree root for the current branch. Tests cover nested checkouts, linked worktrees, and both core.worktree configurations.

Changes

Git worktree path handling

Layer / File(s)	Summary
Separate Git directory filtering apps/server/src/vcs/GitVcsDriverCore.ts	readGitRefsSnapshot no longer treats the shared Git directory as a reusable worktree. Other entries still require a successful path check.
Current worktree path resolution and coverage apps/server/src/vcs/GitVcsDriverCore.ts, apps/server/src/vcs/GitVcsDriverCore.test.ts	listRefs uses the caller’s worktree root for the current branch. Tests cover separate Git directories with and without core.worktree, nested paths, and linked worktrees.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix · Severity of issue fixed: Low

Suggested reviewers: t3dotgg

Merge Risk: ⚪ Minimal · up to eff1b

The updated Git worktree handling preserves the requested checkout path and avoids reusing separate metadata directories. No remaining merge-blocking risk was identified.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: preventing separate Git metadata directories from being treated as worktree paths.
Description check	✅ Passed	The description explains what changed, why it changed, and how it was validated. It includes the required checklist and correctly identifies the server-only scope, so UI evidence is not applicable.
Linked Issues check	✅ Passed	The PR addresses #12204. readGitRefsSnapshot excludes the Git common metadata directory from reusable worktree paths. listRefs uses the caller's --show-toplevel result for the current checkout a…
Out of Scope Changes check	✅ Passed	The changed production code and tests directly support #12204. The test additions verify the Git metadata and requested-folder behavior. No unrelated production behavior or unrelated files are shown i…
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 2…

✨ Finishing Touches

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