[Bug]: Thread worktree keeps the PR branch checked out after the PR is opened, so the user can't check it out in their own clone #36415

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/server

Steps to reproduce

1. Start a thread in a new worktree. Its branch ends up as feature-x (renamed from t3/<id> or chosen by the user).
2. Let the agent commit, push and open a PR for feature-x.
3. In the user's main clone of the same repo, run git checkout feature-x.

Expected behavior

Once the PR is open, the user can check out feature-x in their own clone to review or keep working on it.

Actual behavior

fatal: 'feature-x' is already used by worktree at '~/.t3/worktrees/<project>/<thread-id>'

The thread's worktree keeps feature-x checked out until the user switches it away by hand. I haven't isolated whether the worktree holds the branch from creation or only from the PR onward. Either way, it still holds the branch after the PR is open.

The only workaround is git switch --detach in the thread's worktree, and it causes two more problems:

• T3 keeps the old branch name for the thread. After detaching, t3_worktree_status still returns { "attached": true, "branch": "feature-x" } (similar to [Bug]: Thread in the project folder keeps its starting branch and MR after the agent runs git checkout #33278).
• Cleanup will never remove the worktree. Because the recorded branch no longer matches what's checked out, every cleanup pass keeps it with "Repository or branch changed" ([Bug]: Worktree cleanup never removes a worktree whose branch was renamed, switched, or detached #17813).

So right now the user has to choose between being able to check out their branch and having worktrees cleaned up.

Suggested fix

• After a PR is opened (or when the thread settles), release the branch: detach the worktree and update the thread's recorded branch to match, so the worktree still qualifies for cleanup under [Bug]: Worktree cleanup never removes a worktree whose branch was renamed, switched, or detached #17813's rules.
• Or keep thread worktrees on a T3-owned ref and push with HEAD:refs/heads/<pr-branch>, so the user's branch is never checked out by T3.

Impact

Major degradation: it happens on every thread whose branch the user later wants to check out locally.

Version or commit

T3 Code 0.1.10-nightly.20261113.4643 (9a35ab0), desktop

Environment

macOS, Claude agent, Bitbucket-hosted repo

Related

#17813, #33278, #33397