Add tests for previously uncovered code paths in infrastructure.events.bus:
- TestSingletonHelpers: get_event_bus() singleton, init_event_bus_persistence()
(idempotency and default-path behaviour), and module __getattr__ error path
- TestEventBusPersistence: exception-swallowing in _persist_event() and replay()
(lines 143-144 and 200-202) via patched contextmanager
Coverage: 92.7% → 99.3% (38 tests, all passing).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>