Fixing Flaky Tests

Target symptom: Tests pass when run alone, fail when run with other tests.

Diagnose first

Test passes alone, fails with others?
    │
    ├─ Same error every time → Shared state
    │   └─ Database, globals, files, singletons
    │
    ├─ Random/timing failures → Race condition
    │   └─ Use `condition-based-waiting` skill
    │
    └─ Resource errors (port, file lock) → Resource conflict
        └─ Need unique resources per test/worker