fix(worktree): reuse an existing group branch on resume instead of recreating it

[OGtwelve]

Summary

WorktreePool.acquire always ran git worktree add -b <branch> <base>, which fails outright when the group branch already exists (a resumed run) — or, if recreated from base, drops the prior commits. It now checks out an existing branch instead, preserving committed-but-unpushed work and fixing the resume crash. A brand-new group still branches from base.

Changes

• src/workspace/worktree-pool.ts — branchExists() helper; acquire reuses git worktree add <path> <branch> when the branch exists, else -b <branch> <base>.

Testing

• src/workspace/worktree-pool.test.ts: integration test creating a branch with a commit, removing its worktree, then acquiring — asserts the prior commit/file is checked out. Existing fresh-branch path unchanged. Full suite green (672); biome + tsc clean.

Note

Auto-opening a PR for the recovered work when a resumed task then blocks is a smaller follow-up.

Refs #77

Summary by CodeRabbit

• Bug Fixes
  • Resuming a workspace now reuses an existing branch when available, instead of trying to create a duplicate one.
  • Previously committed changes in a removed temporary workspace are now preserved and restored on the next checkout.
  • This helps resumed runs continue from the last saved state without losing work or failing during setup.

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Review details

⚙️ Run configuration

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Pro

Run ID: a9f0f9ab-bc2c-4dc2-a766-13aad3549f79

📥 Commits

Reviewing files that changed from the base of the PR and between 607c267 and d862c98.

📒 Files selected for processing (2)

• packages/aitm/src/workspace/worktree-pool.test.ts
• packages/aitm/src/workspace/worktree-pool.ts

📝 Walkthrough

Walkthrough

WorktreePool.acquire() gains a branchExists helper that checks refs/heads/<branch> via git rev-parse --verify --quiet. When the ref exists, acquire() reuses it with git worktree add <path> <branch>; otherwise it creates a fresh branch with -b. A new test validates the resume scenario end-to-end.

Changes

WorktreePool Branch Reuse on Resume

Layer / File(s)	Summary
branchExists helper and acquire() conditional logic packages/aitm/src/workspace/worktree-pool.ts	Adds branchExists(repoRoot, branch) that runs git rev-parse --verify --quiet refs/heads/<branch>. Updates acquire() to use the reuse form of git worktree add when the branch ref exists, or the create-and-track form otherwise.
Resume mode integration test packages/aitm/src/workspace/worktree-pool.test.ts	Imports readFile/writeFile and adds a test that seeds a prior commit on a group branch, removes the worktree, reacquires via WorktreePool.acquire, and asserts the prior file content and commit message are present.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related issues

• Partial group work can be stranded on crash-recovery (committed-but-unpushed tasks) #77: This PR directly implements the fix for the crash/data-loss scenario where acquire() would fail or discard committed-but-unpushed work when a group branch ref already existed after a resumed run.

Possibly related PRs

• developerz-ai/ai-task-master#6: Directly touches WorktreePool.acquire() and the git worktree add branch-handling logic in the same file.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately captures the main change: reusing an existing group branch during resume instead of recreating it.
Docstring Coverage	✅ Passed	Docstring coverage is 50.00% which is sufficient. The required threshold is 30.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/worktree-reuse-branch-77

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Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@packages/aitm/src/workspace/worktree-pool.ts`:
- Around line 35-38: The branchExists() helper is swallowing all git rev-parse
failures and treating them as a missing branch, which can send acquire() down
the wrong git worktree add path. Update branchExists in worktree-pool.ts to
catch only the specific missing-ref case from runGit(['rev-parse', '--verify',
'--quiet', ...]) and rethrow any other repo, permission, or runtime errors so
callers can distinguish real failures from an absent branch.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Pro

Run ID: 0b149be9-d472-47a8-b073-292d9519816d

📥 Commits

Reviewing files that changed from the base of the PR and between 7140325 and 607c267.

📒 Files selected for processing (2)

• packages/aitm/src/workspace/worktree-pool.test.ts
• packages/aitm/src/workspace/worktree-pool.ts

[OGtwelve]

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