- lagoon.Transaction, the lagoon:after_commit flush and the immediate
AfterCommit path pass a handle with an empty statement on the write's
connection (Session NewDB+Context, Clauses(), Session NewDB)
- a WithContext query through the handle no longer continues from the
written model's statement (deferred from 11-05)
- TestTransactionAfterCommit/callback_handle_has_a_clean_statement covers
the implicit, plain-transaction and lagoon.Transaction paths
- 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
