[Bug]: Started with GIT_DIR set, T3 Code shows another repository's branch in my project #35099

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. Make two repositories:

   git init -b main demo-project && cd demo-project
   echo "# Demo project" > README.md && git add README.md && git commit -m "Initial commit"
   git switch -c feature/demo-project && cd ..
   git init -b main inherited-other && cd inherited-other
   echo "# Other repository" > OTHER.md && git add OTHER.md && git commit -m "Other initial commit"
   git switch -c wrong-repository-branch && cd ..

2. Start the T3 Code server with GIT_DIR pointing at the second repository, as it is when the server is started from a Git hook (Git exports GIT_DIR to hook scripts). From a source checkout: GIT_DIR=/path/to/inherited-other/.git vp run dev.
3. Add demo-project as a project (Add project > Local folder) and look at the thread details panel and its branch picker.

Expected behavior

demo-project shows its own branch, feature/demo-project, and no changes. That is what the same steps show when the server starts without GIT_DIR.

Actual behavior

demo-project shows the branch wrong-repository-branch, and its branch picker lists wrong-repository-branch (current) and main, the branches of inherited-other. Changes shows +1 -1 although demo-project has no changes.

Impact

Minor bug or occasional failure

Version or commit

main, commit b68aedf

Environment

Linux, web client in Chromium, dev server from source with a fresh home, Node 26.12.1, git 2.53.

Logs or stack traces

Screenshots, recordings, or supporting files

main b68aedf: started with GIT_DIR set, demo-project shows wrong-repository-branch and the other repository branches

Workaround

Unset GIT_DIR before starting T3 Code.

A fix is in #28795.