Static assertions on the committed ledger source (idempotent table DDL,
parameterized idempotent record, has/applied queries, driver-boundary
re-export, CI enforcement) with mutation probes proving non-vacuousness;
docker-gated real-stack probe migrates an empty database (isolated compose
project + host port) and confirms the ledger exists, the applied migrations
are recorded, and a re-run records nothing twice. New additive
database-postgres-ledger CI job gates the criterion on every PR.
