Git worktree conflict when master is checked out elsewhere

If master is checked out in another worktree, any local operation that checks it out fails with fatal: 'master' is already used by worktree ...; this is not an auth or branch-protection failure. For PR merges, use the GitHub API admin merge, e.g. gh api PUT /repos/getsentry/craft/pulls/{n}/merge -f merge_method=squash, which avoids local checkout. For post-merge cleanup, detach at the merge commit (git checkout <merge-commit-sha>) before deleting the branch rather than checking out master. Verify merge and remote-branch state separately.