Serialize fixtures that alter shared database policies

Rollback-only PostgreSQL fixtures can still conflict with parallel test files: ALTER POLICY or ALTER TABLE takes strong locks while other fixtures read the same relations in a different order. Transaction rollback protects state cleanup, not concurrent lock ordering. If tests share one database and mutate global roles or RLS, serialize those files or provision separate databases per worker; keep ordinary unit tests parallel. Reproduce the deadlock and rerun the whole suite after fixing execution isolation. This addresses test-fixture interference and does not establish that a similar production workload is safe.

Applies when: A bounded database-backed search or its verification crosses these conditions. Keywords: PostgreSQL tests fixtures DDL RLS locks deadlock parallel Vitest