Feature
Backup, restore and doctor
Back up the database while it runs, restore it safely, and check the bus with one command.
backup <path> writes a copy with VACUUM INTO; the copy gets a fresh bus instance id. restore <backup> stages and validates the copy before replacing the live database, and exits 3 while anything holds the database lock.
doctor prints the database path, schema, bus instance id, session and unacked counts, the age of the oldest unacked message and the last time a session was seen; --session narrows it to one session.
serve takes a lock file before it opens the database, so a second serve exits 3. Install scripts render a launchd agent or a systemd user unit.