Pure reference catalog of test-isolation and fixture-lifecycle patterns - the four-phase test pattern (Meszaros), fixture scope (per-test / per-describe / shared / global), the Fresh-Fixture vs Shared-Fixture trade-off (Fowler), parallel-safety patterns, and cleanup discipline (afterEach / afterAll / tagged-cleanup), plus a pattern-selection guide and a worked leaking-state diagnosis. The database-isolation strategies (transaction-rollback / database-per-worker / template-database) and network / external-service stubbing live in references/. This is the architecture-tier reference, not a file-level fixture-coupling style rule. Use when designing fixture scope and isolation strategy, auditing fixture coupling or retry/wait policy, or moving a suite to parallel execution.