App becomes unresponsive while polling sessions whose PR branches were merged and deleted

Report from GitHub Copilot on behalf of...

Environment:

• GitHub Copilot App build 1.0.80
• Windows
• Worktree-backed project sessions

Observed behavior:
After a project session’s pull request is merged and its upstream branch is deleted, leaving that session active/unarchived appears to cause the App to continue polling it. The UI then repeatedly hangs or becomes unresponsive.

This occurred with multiple completed project sessions. The affected prior session was named 2026-09-03 (session ID 074d6dc2-7a4f-4e1d-88ca-bc7368a082c6).

Archiving the stale session and moving coordination to a clean session based on the repository’s current default branch appears to stop the problem.

Expected behavior:
When a tracked PR is merged and its branch disappears, the App should stop or safely back off polling, mark the session as completed/stale, or prompt the user to archive it. A dead upstream must not make the UI unresponsive.

Approximate reproduction:

1. Create a worktree-backed project session.
2. Open and merge its pull request.
3. Delete the merged remote branch.
4. Leave the project session active rather than archiving it.
5. Continue using the App while it checks the session’s PR/branch state.
6. Observe repeated UI hangs or unresponsiveness.

Impact:
The App becomes difficult or impossible to use and requires archiving the completed session or moving work into a clean successor session.

Workaround:
Archive completed sessions promptly after their PR branches are merged/deleted, then continue from a clean default-branch session.

Notes:

• This is observed as a UI hang/unresponsiveness problem; a full process crash has not been confirmed.
• Continued polling is the apparent trigger based on behavior, but logs have not yet established the root cause.
• I have not deliberately reproduced the hang again because it disrupts active work.

No source files or tests are named. Start by tracing the polling path for active worktree-backed sessions and the UI handling of merged pull requests whose remote branches were deleted; reproduce with the listed six-step sequence if possible. Done means the App no longer hangs and safely stops, backs off, marks stale, or prompts for archival when the tracked branch disappears.