test(db): prove PostgreSQL retirement atomicity

docs/RELEASE_DEPENDENCIES.md

@@ -788,7 +788,18 @@ tools/checks/postgres-integration-check.py \
 The script checks migrations and `/health` startup for core-only, files-only,
 mail-only, campaign-only, campaign+files, campaign+mail, and full-product
 module sets. `--reset-schema` is destructive and must only be used against a
-throwaway database.
+throwaway database. Before those permutations, the required Core proof runs in
+random, test-owned schemas without modifying `public`. It exercises Files' real
+credential-owning retirement provider and proves that credential scrubbing,
+non-secret audit
+insertion, and table retirement commit together; database-injected audit and
+DDL failures roll the entire unit back. A 500 ms PostgreSQL `lock_timeout` and
+captured backend process IDs also prove that each `DROP TABLE` uses the
+installer Session connection instead of waiting through a second connection.
+The meta check enables the release-gate flag so missing PostgreSQL configuration
+or full-stack test packages are a hard failure; ordinary Core-only test discovery
+skips this integration proof. Do not pass `--skip-retirement-atomicity` when
+collecting release evidence.
 
 ## Migration Baselines