worktree-cleanup

Verify the merge by comparing `git merge-tree --write-tree origin/master <branch>` with `git rev-parse origin/master^{tree}`; equal SHAs mean the work landed. Then run prune_worktrees.py --prune to remove the merged, clean, unlocked worktree.

Squash and rebase merges land content under new SHAs, so the tool sees commits on the branch and cannot distinguish landed work from unlanded work. Verify by tree content instead of passing discard_changes, which risks deleting real unlanded work.

git branch -d succeeds while the local tracking ref still carries the branch tip, because it checks merge status against HEAD or the upstream. The window closes at the next git fetch --prune, after which only -D works.

Avoid bare git stash and git stash pop because the stash stack and index are shared across all worktrees and concurrent sessions. Prefer a temporary WIP commit, or stash with a unique message and restore via git stash apply <sha>.

Removing a worktree makes its branch's objects unreachable, but git gc --auto only runs above loose-object and pack thresholds, so churn accumulates. Running prune_worktrees.py --gc drops unreachable objects older than a day and clears stale gc.log files.