Deleting squash-merged branches safely: compare local head to the merged PR's headRefOid

After squash merges, git branch -d refuses (branch isn't an ancestor of master) and [gone] upstream alone doesn't prove nothing was added after the merge. Check gh pr view <n> --json headRefOid against git rev-parse <branch>; if they match, git branch -D loses nothing. Branches listed by git branch --merged origin/master can use plain -d. Leave remote-only branches with no PR for the user (remote delete is not undoable from local), and don't touch untracked files another session may be writing.