fix: bound SQLite WAL growth and prevent worker hangs (#49)

The worker's SQLite WAL could grow unbounded (observed 19MB) and wedge the
DB, hanging Claude Code on every prompt. No checkpoint ever truncated the
WAL (only PASSIVE auto-checkpoint, which cannot reclaim the file), the
connection-scoped pragmas were set via a single Exec so only one pooled
connection received them (e.g. busy_timeout=0 on the rest), and the
maintenance service that would optimize/checkpoint was never wired up.

- Register a sqlite3 ConnectHook driver so all pragmas (busy_timeout,
  journal_mode, synchronous, cache_size, foreign_keys, journal_size_limit)
  apply to every pooled connection; enable safe connection recycling.
- Add Store.Checkpoint (TRUNCATE), checkpoint-on-Close, and a periodic
  size-gated checkpoint loop with configurable interval/threshold.
- Wire up the previously-dead maintenance service; make trigger_maintenance
  actually run DB maintenance instead of only recalculating scores.
- Harden the user-prompt hook to honor its deadline and fail open so a
  slow worker can never stall a prompt.
- Add regression tests for WAL truncation, checkpoint-on-close, and
  per-connection pragmas.

internal/maintenance/service.go

@@ -83,8 +83,20 @@ func (s *Service) Start(ctx context.Context) {
 		Bool("cleanup_stale", s.config.CleanupStaleObservations).
 		Msg("Starting maintenance scheduler")
 
-	// Initial run after 5 minutes (allow system to stabilize)
-	time.Sleep(5 * time.Minute)
+	// Initial run after 5 minutes (allow system to stabilize).
+	// Use a cancellable timer so shutdown (ctx cancel / Stop) is not blocked for up to 5m.
+	initialDelay := time.NewTimer(5 * time.Minute)
+	select {
+	case <-ctx.Done():
+		initialDelay.Stop()
+		s.log.Info().Msg("Maintenance shutting down before initial run (context cancellation)")
+		return
+	case <-s.stopCh:
+		initialDelay.Stop()
+		s.log.Info().Msg("Maintenance shutting down before initial run (stop signal)")
+		return
+	case <-initialDelay.C:
+	}
 	s.runMaintenance(ctx)
 
 	ticker := time.NewTicker(interval)
@@ -288,7 +300,13 @@ func (s *Service) Stats() map[string]any {
 	}
 }
 
-// RunNow triggers an immediate maintenance run.
+// RunNow triggers an immediate maintenance run in the background.
 func (s *Service) RunNow(ctx context.Context) {
 	go s.runMaintenance(ctx)
 }
+
+// RunNowSync triggers an immediate maintenance run and blocks until it completes.
+// Use this when the caller needs to report a synchronous result (e.g. an HTTP handler).
+func (s *Service) RunNowSync(ctx context.Context) {
+	s.runMaintenance(ctx)
+}