feat(server): emit playlist.system_rebuilt on daily + manual system-playlist rebuild

The daily 03:00 scheduler rebuild (and the manual refresh endpoint) replace
a user's system playlists + You-might-like rows but published no event, so a
client left open across the rebuild served yesterday's snapshot until a
manual reload — the stale-tab case behind #968. Add a user-scoped
playlist.system_rebuilt event (envelope {kind,user_id,data:{}}) from both the
scheduler (bus threaded into NewScheduler) and handleSystemPlaylistRefresh.
Clients consume it to invalidate home / system-playlist views and proactively
re-pull a stale active queue. Issue #968.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

cmd/minstrel/main.go

@@ -242,7 +242,12 @@ func run() error {
 	// active user's daily build at 03:00 in their stored timezone.
 	// Replaces the 24h-anchored cron loop (removed in the next commit
 	// of this arc).
-	playlistScheduler, err := playlists.NewScheduler(pool, logger.With("component", "playlist_scheduler"), cfg.Storage.DataDir)
+	playlistScheduler, err := playlists.NewScheduler(
+		pool,
+		logger.With("component", "playlist_scheduler"),
+		cfg.Storage.DataDir,
+		bus,
+	)
 	if err != nil {
 		return fmt.Errorf("init playlist scheduler: %w", err)
 	}

internal/api/events_publish.go

@@ -88,6 +88,21 @@ func (h *handlers) publishPlaylistEvent(kind string, ownerID, playlistID pgtype.
 	})
 }
 
+// publishSystemRebuilt notifies the owner's clients that their system
+// playlists (and You-might-like rows) were regenerated, so they invalidate
+// the home / system-playlist providers and a stale active queue can re-pull.
+// Mirrors the daily scheduler's event; fired here from the manual refresh.
+func (h *handlers) publishSystemRebuilt(userID pgtype.UUID) {
+	if h.eventbus == nil {
+		return
+	}
+	h.eventbus.Publish(eventbus.Event{
+		Kind:   "playlist.system_rebuilt",
+		UserID: uuidToString(userID),
+		Data:   map[string]any{},
+	})
+}
+
 // publishRequestStatusChanged broadcasts a Lidarr request status flip to
 // the request's original requester so their /requests page reflects the
 // new state without manual refresh. Admin actors (approve / reject) still

internal/api/playlists_system_shuffle.go

@@ -73,6 +73,8 @@ func (h *handlers) handleSystemPlaylistRefresh(w http.ResponseWriter, r *http.Re
 		writeErr(w, apierror.InternalMsg("build failed", err))
 		return
 	}
+	// #968: announce the rebuild so the user's other clients refresh.
+	h.publishSystemRebuilt(user.ID)
 	q := dbq.New(h.pool)
 	v := kind
 	pl, err := q.GetSystemPlaylistByVariantForUser(r.Context(),

internal/playlists/scheduler.go

@@ -28,6 +28,7 @@ import (
 	"github.com/jackc/pgx/v5/pgxpool"
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/eventbus"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/taste"
 )
 
@@ -47,14 +48,21 @@ type Scheduler struct {
 	pool    *pgxpool.Pool
 	logger  *slog.Logger
 	dataDir string
+	bus     *eventbus.Bus // #968: announce rebuilds so clients self-refresh
 
 	mu   sync.Mutex
 	jobs map[pgtype.UUID]uuid.UUID // user_id → gocron job id
 }
 
 // NewScheduler builds an idle scheduler. Caller must invoke Start
-// before any builds fire.
-func NewScheduler(pool *pgxpool.Pool, logger *slog.Logger, dataDir string) (*Scheduler, error) {
+// before any builds fire. bus may be nil (tests); rebuild events are
+// then skipped.
+func NewScheduler(
+	pool *pgxpool.Pool,
+	logger *slog.Logger,
+	dataDir string,
+	bus *eventbus.Bus,
+) (*Scheduler, error) {
 	g, err := gocron.NewScheduler()
 	if err != nil {
 		return nil, fmt.Errorf("init gocron: %w", err)
@@ -64,6 +72,7 @@ func NewScheduler(pool *pgxpool.Pool, logger *slog.Logger, dataDir string) (*Sch
 		pool:    pool,
 		logger:  logger,
 		dataDir: dataDir,
+		bus:     bus,
 		jobs:    map[pgtype.UUID]uuid.UUID{},
 	}, nil
 }
@@ -234,7 +243,26 @@ func (s *Scheduler) rebuildUserDaily(ctx context.Context, userID pgtype.UUID, no
 	if err := BuildSystemPlaylists(ctx, s.pool, s.logger, userID, now, s.dataDir); err != nil {
 		s.logger.Warn("scheduler: build failed",
 			"user_id", uuidStringPL(userID), "err", err)
+		return
 	}
+	// #968: tell the user's connected clients their home content was
+	// regenerated, so a tab/app left open across the rebuild refreshes its
+	// system-playlist + You-might-like views (and a stale active queue can
+	// re-pull) instead of serving yesterday's snapshot until a manual reload.
+	s.publishRebuilt(userID)
+}
+
+// publishRebuilt broadcasts a user-scoped "system playlists rebuilt" event.
+// No-op when the bus is nil (test construction).
+func (s *Scheduler) publishRebuilt(userID pgtype.UUID) {
+	if s.bus == nil {
+		return
+	}
+	s.bus.Publish(eventbus.Event{
+		Kind:   "playlist.system_rebuilt",
+		UserID: uuidStringPL(userID),
+		Data:   map[string]any{},
+	})
 }
 
 // Stop drains gocron and stops the scheduler loop.