PostgreSQL-native one-statement commitment for a claimed runtime moment.
The checkpoint fence, immutable run binding, scoped run update, assigned event insert, and optional wake notification execute as one PostgreSQL statement. PostgreSQL statement atomicity makes the run update and event insert indivisible without an explicit transaction.
A zero-row update pays one diagnostic read to preserve the public
:not_found / :invalid_commit / :stale_fence distinction. The
successful hot path performs exactly one database exchange.