[Bug]: Worktree reuse silently breaks on Git < 2.36 (git worktree list --porcelain -z fails, all refs lose worktreePath)

[didiez]

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. Use a machine with Git < 2.36 (mine: Ubuntu 22.04.3 LTS, stock git 2.34.1; it is the current version in Ubuntu 22.04's repos, so this affects every default 22.04 box).
2. In a project, leave the main checkout on main and create a worktree:
   git worktree add ~/wt/feat-x -b feat-x
3. In T3 Code, start a new thread on that project with Workspace = Current checkout.
4. Open the branch picker and select feat-x.

Expected behavior

feat-x shows the worktree badge in the picker, and selecting it takes the reuseExistingWorktree path: the thread is bound to ~/wt/feat-x, no git command is run, the workspace chip becomes "Current worktree", and no second worktree is created on send.

Actual behavior

No worktree badge is shown on any branch. Selecting feat-x runs git checkout feat-x in the main checkout, which Git correctly refuses:

Git command failed in GitVcsDriver.switchRef.checkout (<project path>): git checkout failed

The real Git message (fatal: 'feat-x' is already checked out at '<worktree path>') never reaches the user — see "secondary issues" below — so the error looks like a T3 worktree bug rather than a Git version problem.

Impact

Major degradation or frequent failure

Version or commit

0.0.43-nightly.20260920.2005

Environment

Ubuntu 22.04.3 LTS

Logs or stack traces

Git command failed in GitVcsDriver.switchRef.checkout (<project path>): git checkout failed

# what git actually said, obtained by hand:
fatal: 'feat/<branch>' is already checked out at '<home>/.t3/worktrees/<project>/<worktree>'

Screenshots, recordings, or supporting files

No response

Workaround

Upgrade Git to ≥ 2.36 on the machine that hosts the project (verified fixed with Git 2.55.0 from ppa:git-core/ppa; the worktree badges reappear and branch selection binds the thread to the existing worktree with no checkout).

[juliusmarminge]

This matches open PR #12263 (git worktree list --porcelain -z fallback for Git < 2.36). That PR now has Closes #12761.

Related secondary (opaque git stderr): #4380