feat(api): My Wave sessions with a Go fallback and wave metrics (M4)

- /wave/options, POST /wave/sessions (activity, mood, seed),
  /next with reactions, PATCH to switch the context on the fly, DELETE
- the recommender is called with an 800 ms budget; on failure the api
  serves a fallback wave of likes, favourite artists and random
  available tracks with the same dislike / recent / served filters
- every served track is an impression with its source and model; wave
  events (context_type wave) set its outcome, reactions win
- library status shows the analysis queue and 7-day wave metrics:
  listen-through, early skip and like rate

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

services/api/internal/library/handler.go

@@ -261,6 +261,14 @@ func (h *Handler) GetLibraryStatus(ctx context.Context, _ gen.GetLibraryStatusRe
 	out := gen.GetLibraryStatus200JSONResponse{
 		Artists: int(c.Artists), Albums: int(c.Albums), Tracks: int(c.Tracks), Files: int(c.Files),
 		MissingFiles: int(c.Missing), FileErrors: int(c.Errors), Sources: []gen.SourceStatusItem{},
+		Analysis: gen.AnalysisStatus{
+			Queued: st.Analysis.Queued, Running: st.Analysis.Running, Done: st.Analysis.Done,
+			Failed: st.Analysis.Failed, AnalyzerVer: st.Analysis.AnalyzerVer,
+		},
+		Wave: gen.WaveMetrics{
+			Served: st.Wave.Served, Sessions: st.Wave.Sessions, ListenThroughRate: st.Wave.ListenThrough,
+			EarlySkipRate: st.Wave.EarlySkip, LikeRate: st.Wave.LikeRate,
+		},
 	}
 	for _, s := range st.Sources {
 		dto := h.sourceDTO(s)

services/api/internal/library/service.go

@@ -576,8 +576,10 @@ func (s *Service) startScan(src Source, full bool) error {
 
 // Status — состояние библиотеки (admin, moderator).
 type Status struct {
-	Counts  Counts
-	Sources []Source
+	Counts   Counts
+	Sources  []Source
+	Analysis AnalysisCounts
+	Wave     WaveMetrics
 }
 
 // Status собирает счётчики и состояние источников.
@@ -593,7 +595,15 @@ func (s *Service) Status(ctx context.Context) (Status, error) {
 	if err != nil {
 		return Status{}, err
 	}
-	return Status{Counts: c, Sources: sources}, nil
+	analysis, err := s.store.AnalysisCounts(ctx)
+	if err != nil {
+		return Status{}, err
+	}
+	wave, err := s.store.WaveMetrics(ctx)
+	if err != nil {
+		return Status{}, err
+	}
+	return Status{Counts: c, Sources: sources, Analysis: analysis, Wave: wave}, nil
 }
 
 // FileErrors — файлы с ошибками чтения.

services/api/internal/library/store.go

@@ -574,3 +574,52 @@ func (st *Store) AlbumCoverPath(ctx context.Context, albumID uuid.UUID) (*string
 	}
 	return p, nil
 }
+
+// AnalysisCounts — состояние очереди аудиоанализа.
+type AnalysisCounts struct {
+	Queued, Running, Done, Failed int
+	AnalyzerVer                   *string
+}
+
+// AnalysisCounts считает задачи анализа по статусам и текущую версию анализатора.
+func (st *Store) AnalysisCounts(ctx context.Context) (AnalysisCounts, error) {
+	var c AnalysisCounts
+	err := st.pool.QueryRow(ctx, `
+		SELECT count(*) FILTER (WHERE status = 'queued'), count(*) FILTER (WHERE status = 'running'),
+			count(*) FILTER (WHERE status = 'done'), count(*) FILTER (WHERE status = 'failed'),
+			(SELECT analyzer_ver FROM track_features ORDER BY analyzed_at DESC LIMIT 1)
+		FROM analysis_jobs`).Scan(&c.Queued, &c.Running, &c.Done, &c.Failed, &c.AnalyzerVer)
+	if err != nil {
+		return AnalysisCounts{}, fmt.Errorf("library: analysis counts: %w", err)
+	}
+	return c, nil
+}
+
+// WaveMetrics — метрики волны за 7 дней (docs/recommendations.md#1-цели-и-как-измеряем-успех).
+type WaveMetrics struct {
+	Served, Sessions                   int
+	ListenThrough, EarlySkip, LikeRate *float32
+}
+
+// WaveMetrics считает метрики по показам с известным исходом.
+func (st *Store) WaveMetrics(ctx context.Context) (WaveMetrics, error) {
+	var (
+		m                             WaveMetrics
+		judged, through, early, liked int
+	)
+	err := st.pool.QueryRow(ctx, `
+		SELECT count(*), count(DISTINCT wave_session_id), count(outcome),
+			count(*) FILTER (WHERE outcome IN ('complete', 'like')),
+			count(*) FILTER (WHERE outcome IN ('skip_early', 'dislike')),
+			count(*) FILTER (WHERE outcome = 'like')
+		FROM wave_impressions WHERE served_at > now() - interval '7 days'`).
+		Scan(&m.Served, &m.Sessions, &judged, &through, &early, &liked)
+	if err != nil {
+		return WaveMetrics{}, fmt.Errorf("library: wave metrics: %w", err)
+	}
+	if judged > 0 {
+		lt, es, lr := float32(through)/float32(judged), float32(early)/float32(judged), float32(liked)*100/float32(judged)
+		m.ListenThrough, m.EarlySkip, m.LikeRate = &lt, &es, &lr
+	}
+	return m, nil
+}