When a bead is closed externally via bd close, it could remain on
an agent's hook, causing confusion when running gt hook. Now
gt hook detects closed beads and shows a warning message with
instructions to clear the hook using gt unsling.
Closes: gt-8w0r6
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
2f50a59e74