Postgres FK "update or delete violates foreign key constraint" on audit table during integration test teardown — fix is ON DELETE SET NULL, not test reordering

Integration tests fail with PostgresError: update or delete on table "X" violates foreign key constraint "Y_fkey" on table "Z" when the teardown deletes a parent row (e.g., a test agent/user). Latent for months because the audit/event table only got rows from rarely-fired async jobs. Becomes flaky-then-broken the moment a new code path writes those audit rows synchronously on the same code path the test exercises. Symptom: one test file fails first, but 10+ other test files have the same latent dependency.

Root cause: the FK on the audit/event table was declared without an explicit ON DELETE clause, so Postgres defaulted it to RESTRICT. The schema definition looks innocuous: agent_id text REFERENCES agents(id). Drizzle equivalent: .references(() => agents.id) with no second arg. For audit/event tables, set ON DELETE SET NULL on the agent/user FK — the event happened and should be preserved, but the FK does not need to stay valid once the referenced row is gone. Postgres does NOT support altering ON DELETE in place, so the migration must DROP and re-ADD the constraint:

ALTER TABLE privacy_events DROP CONSTRAINT IF EXISTS privacy_events_agent_id_fkey; ALTER TABLE privacy_events ADD CONSTRAINT privacy_events_agent_id_fkey FOREIGN KEY (agent_id) REFERENCES agents(id) ON DELETE SET NULL;

Also update the ORM schema annotation. Drizzle: .references(() => agents.id, { onDelete: 'set null' })

Do NOT fix by reordering the test teardown to delete audit rows first. That only patches one test file; every other test file deleting the parent has the same latent bug. Fix the schema once. ON DELETE CASCADE is wrong for audit tables (loses history); SET NULL is right.

How to find similar latent FKs before they bite: grep migrations for REFERENCES <parent>(id) lines without ON DELETE and audit each. Tables created with default RESTRICT but written only from rarely-fired code paths are time bombs.