- OnDatabase runs a callback once the database is published (now, or when
lagoon.Publish runs), so GORM callbacks registered at Boot also install
under serve, where Boot runs before the database is opened
- Transaction runs AfterCommit callbacks in order after a successful commit;
nested calls are savepoints whose callbacks drop with them
- the lagoon:after_commit GORM callback flushes single-statement AfterCommit
work after GORM's own commit; outside a transaction it runs immediately
