fix(server): keep worktree creation working when git config is locked

[Gigioxx]

A held .git/config.lock can make worktree creation report failure after Git has already created a usable checkout. This also happens when concurrent config writers briefly contend for the lock.

Make only the optional branch.<new>.gh-merge-base write best-effort. Keep main's current branch resolver, warn on its typed Git command failure, and return the checkout. Required worktree failures, defects, and cancellation still propagate; missing metadata uses the existing base-branch fallback. The shared Git driver covers thread bootstrap and direct worktree creation for all clients and providers.

Fixes #11735. Scope follows the maintainer triage. Original implementation and regression by @Gigioxx in #11773; maintainer takeover merged current main while retaining the contributor's commits.

Verification:

• Before: the deterministic real-Git regression fails against main at configureBaseRef with exit 255 after checkout succeeds.
• After: 33 relevant tests pass in GitVcsDriverCore.test.ts (worktree|worktrees|resolveBranchName); the locked-config regression verifies returned path/branch, checked-out content, absent optional metadata, and the untouched lock. PR tests remain 1 → 1.
• Server typecheck, scoped lint, formatting, and diff checks pass. Lint reports two existing warnings.
• No UI change; proof is through the real Git driver and temporary repositories, not screenshots. No provider was invoked.
• Not verified on macOS, Windows/WSL, iOS, Android, or Electron desktop. The lock test is deterministic, not a parallel timing stress test. No direct optional-write interruption test was added.

Independent full-diff review: one parallel round with Claude Opus 5.5 and GPT-6-Sol; both returned no findings. Claude also ran four additional focused tests successfully.

Model/harness: GPT-6.1-Sol implementation and GPT-6-Astra tests through Codex in T3 Code; independent Claude Opus 5.5 and GPT-6-Sol reviews through T3 Code.

[macroscopeapp]

Approvability

Verdict: Approved at 4f319b2

Macroscope's review found this PR approvable — This is a focused server bug fix that preserves usable worktrees when an optional Git metadata write fails, while leaving required worktree failures unchanged. The added integration test covers the locked-config scenario and verifies the resulting checkout.

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

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

createWorktree now treats gh-merge-base configuration as best effort. A locked .git/config no longer prevents worktree creation, and a test verifies the worktree remains valid while the lock file is unchanged.

Changes: Worktree base-ref resilience

Layer / File(s)	Summary
Best-effort base-ref configuration and validation apps/server/src/vcs/GitVcsDriverCore.ts, apps/server/src/vcs/GitVcsDriverCore.test.ts	createWorktree catches base-ref configuration failures, logs a warning, and completes successfully. The test covers creation with an existing .git/config.lock, expected worktree contents, missing gh-merge-base, and preservation of the lock file.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: t3dotgg

Merge Risk: ⚪ Minimal · up to fc743

Worktree creation remains available when optional base metadata cannot be written, with no actionable merge-blocking risk identified.

Pre-merge checks: 5

Check name	Status	Explanation
Linked Issues check		The change satisfies #11735. createWorktree now catches failure from the optional branch.<new>.gh-merge-base configuration, logs a warning, and returns the created worktree. The git worktree add…
Out of Scope Changes check		The changes are limited to GitVcsDriver.createWorktree and its regression test. Both changes directly support #11735. No unrelated product behavior or files were changed.
Docstring Coverage		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…
Title check		The title clearly and concisely describes the main fix: worktree creation continues when Git configuration is locked.
Description check		The description covers the problem, implementation, linked issue and maintainer approval, verification results, limitations, and agent details. It omits the template's explicit section headings, but t…

Full details: Linked Issues check

Explanation

The change satisfies #11735. createWorktree now catches failure from the optional branch.<new>.gh-merge-base configuration, logs a warning, and returns the created worktree. The git worktree add and checkout path remains outside this catch, so required checkout failures still propagate. The added regression test verifies the branch, worktree content, missing metadata, and unchanged .git/config.lock. The warning retains the Git error as cause, which preserves diagnostic details such as Git stderr. Cancellation behavior is not changed by this failure-only catch.

Full details: Docstring Coverage

Explanation

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 files.

Full details: Description check

Explanation

The description covers the problem, implementation, linked issue and maintainer approval, verification results, limitations, and agent details. It omits the template's explicit section headings, but the required information is present.

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Dismissing prior approval to re-evaluate fc7431a

[henrikkvamme]

A held lock is not the only trigger. Concurrent worktree creation in one repository causes the same failure, without a sandbox or any lock file left behind.

On 2026-10-09, an app launched three worktree threads into one repository in the same second. One of them failed during workspace preparation:

Workspace preparation failed during provision worktree: Git command failed in GitVcsDriver.createWorktree.configureBaseRef ... Git command exited with a non-zero status

Each createWorktree call writes branch.<new>.gh-merge-base in the main checkout, and every git config write takes .git/config.lock. When two writes overlap, one of them exits 255.

Reproduction in a fresh repository, with git 2.54.0 on macOS:

git init -q
for i in $(seq 1 12); do git config branch.b$i.gh-merge-base main & done; wait

In three runs of 12 parallel writes, 5, 2 and 3 writes failed. All 10 failures were exit 255 with error: could not lock config file .git/config: File exists.

This PR makes the write best-effort, so it also covers the concurrent case. A short retry alone would fix the race, but not a lock that a sandboxed command holds for minutes. That makes this PR the better fix.

[maria-rcks]

Note

Written by claude-opus-5-5 on behalf of Maria

Hi! We are cleaning up open PRs, and this one appears to have been created with an older model (gpt-6). If this change is really important, we recommend rebuilding the PR with a newer model if possible.

[maria-rcks]

Note

Written by claude-opus-5-5 on behalf of Maria

Reopening, this was closed by mistake. Sorry for the noise!

[Gigioxx]

@henrikkvamme Confirmed against current main (63eaa79242), merged cleanly in e12e4703d1: this PR already covers the concurrent branch.<new>.gh-merge-base write failure you described. configureBaseRef catches the Git command failure and returns the successfully created worktree, whether another config writer holds the lock briefly or a sandbox holds it for minutes. No retry is needed to prevent this workspace-preparation failure. Other required worktree-creation errors still propagate; missing optional metadata uses the existing base-branch fallback.

No additional implementation change was needed. The existing regression deterministically holds the real .git/config.lock and verifies the returned worktree, branch, checked-out contents, absent metadata, and untouched lock. After the merge, the focused worktree tests passed (22 passed), server typecheck passed, and scoped lint passed with existing warnings only. This was not a timing-based stress test of parallel creation or a Windows locking test.

GPT-6-Astra via T3 Code, on behalf of Guille

[juliusmarminge]

Taking over this one as maintainer for batch worktree-git-03. I will merge current main, keep the fix focused on optional Git metadata, and verify the locked-config and cancellation behavior. Keeping the original PR; no merge.

Dismissing prior approval to re-evaluate 4f319b2