Slice 3c — completes the server-side producer set.
Publishes scan.run_started when InsertScanRun succeeds and
scan.run_finished after FinishScanRun completes (success or with an
error_message payload). Per-file progress events are intentionally NOT
emitted — they'd flood the stream during large library scans without
giving the admin scan card anything actionable. The two-beat signal
gives the UI enough to invalidate scanStatusProvider at the right
moments.
Bus access uses a package-level setter on internal/library because
threading bus through RunScan + TryStartScan + Scheduler + all their
callers would touch ~10 sites without changing behavior at the boundaries
that don't publish. Per-process singleton, matches the log.SetDefault
idiom. cmd/minstrel/main.go calls library.SetEventBus(bus) once at
startup; test contexts that never call it skip publishing safely
(publishScanEvent is a no-op when bus is nil).
This completes the server side of #392. Slice 4 wires the Flutter
consumer: live_events_provider.dart (StreamProvider) +
live_events_dispatcher.dart (event-kind → provider invalidation)
+ AppLifecycleState cold-start invalidation.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
