Merge pull request 'Release v2026.05.16.0 — recommendations working end-to-end + cover-art uncap' (#50) from dev into main

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

cmd/minstrel/main.go

@@ -105,8 +105,8 @@ func run() error {
 				logger.With("component", "scan_run"),
 				library.RunScanConfig{
 					BackfillCap:     5000,
-					EnrichCap:       cfg.Library.CoverArtBackfillCap,
+					EnrichCap:       -1, // #388: no global cap; per-provider rate limits
-					ArtistEnrichCap: cfg.Library.CoverArtBackfillCap,
+					ArtistEnrichCap: -1,
 					DataDir:         cfg.Storage.DataDir,
 				},
 			); err != nil {
@@ -122,8 +122,8 @@ func run() error {
 				logger.With("component", "scan_run"),
 				library.RunScanConfig{
 					BackfillCap:     5000,
-					EnrichCap:       cfg.Library.CoverArtBackfillCap,
+					EnrichCap:       -1, // #388: no global cap; per-provider rate limits
-					ArtistEnrichCap: cfg.Library.CoverArtBackfillCap,
+					ArtistEnrichCap: -1,
 					DataDir:         cfg.Storage.DataDir,
 				},
 			); err != nil {
@@ -194,8 +194,8 @@ func run() error {
 
 	scanCfg := library.RunScanConfig{
 		BackfillCap:     5000,
-		EnrichCap:       cfg.Library.CoverArtBackfillCap,
+		EnrichCap:       -1, // #388: no global cap; per-provider rate limits
-		ArtistEnrichCap: cfg.Library.CoverArtBackfillCap,
+		ArtistEnrichCap: -1,
 		DataDir:         cfg.Storage.DataDir,
 	}
 	scheduler := library.NewScheduler(pool, logger.With("component", "scheduler"),
@@ -203,7 +203,7 @@ func run() error {
 	scheduler.Start(ctx)
 	srv := server.New(logger, pool, scanner, subsonic.Config{
 		AllowPlaintextPassword: cfg.Subsonic.AllowPlaintextPassword,
-	}, cfg.Events, cfg.Recommendation, cfg.Storage.DataDir, cfg.Branding, coverEnricher, cfg.Library.CoverArtBackfillCap, coverSettings, scanner, scanCfg, scheduler)
+	}, cfg.Events, cfg.Recommendation, cfg.Storage.DataDir, cfg.Branding, coverEnricher, coverSettings, scanner, scanCfg, scheduler)
 	srv.Bus = bus
 	srv.PlaylistScheduler = playlistScheduler
 	httpServer := &http.Server{

flutter_client/pubspec.yaml

@@ -1,7 +1,7 @@
 name: minstrel
 description: Minstrel mobile client
 publish_to: 'none'
-version: 2026.5.15+6
+version: 2026.5.16+8
 
 environment:
   sdk: '>=3.5.0 <4.0.0'

internal/api/admin_covers.go

@@ -48,19 +48,20 @@ func (h *handlers) handleAdminAlbumRefetchCover(w http.ResponseWriter, r *http.R
 }
 
 type adminBulkRefetchResp struct {
-	Queued int `json:"queued"`
+	Started bool `json:"started"`
 }
 
 // handleAdminBulkRefetchCovers implements POST /api/admin/covers/refetch-missing.
-// Returns immediately; actual drain runs in a background goroutine bounded by
+// Returns immediately; the drain runs UNBOUNDED in a background goroutine
-// the configured backfill cap.
+// (#388 — no global cap; remote providers self-throttle per provider, local
+// sources run at disk speed). The count is unknowable synchronously, so the
+// response just acknowledges the drain started.
 func (h *handlers) handleAdminBulkRefetchCovers(w http.ResponseWriter, _ *http.Request) {
-	cap := h.coverArtBackfillCap
 	go func() {
 		bgCtx := context.Background()
-		if _, err := h.coverart.EnrichRetryMissing(bgCtx, cap); err != nil {
+		if _, err := h.coverart.EnrichRetryMissing(bgCtx, -1); err != nil {
 			h.logger.Warn("admin: bulk cover refetch failed", "err", err)
 		}
 	}()
-	writeJSON(w, http.StatusOK, adminBulkRefetchResp{Queued: cap})
+	writeJSON(w, http.StatusOK, adminBulkRefetchResp{Started: true})
 }

internal/api/admin_covers_test.go

@@ -53,7 +53,6 @@ func testHandlersWithCovers(t *testing.T) (*handlers, *coverart.Enricher) {
 	}
 	enricher := coverart.NewEnricher(pool, slog.Default(), settings)
 	h.coverart = enricher
-	h.coverArtBackfillCap = 100
 	return h, enricher
 }
 
@@ -97,7 +96,7 @@ func TestAdminAlbumRefetchCover_AdminOK(t *testing.T) {
 	}
 }
 
-func TestAdminBulkRefetchCovers_AdminReturnsQueuedCount(t *testing.T) {
+func TestAdminBulkRefetchCovers_AdminStartsRefetch(t *testing.T) {
 	if os.Getenv("MINSTREL_TEST_DATABASE_URL") == "" {
 		t.Skip("MINSTREL_TEST_DATABASE_URL not set")
 	}
@@ -115,8 +114,8 @@ func TestAdminBulkRefetchCovers_AdminReturnsQueuedCount(t *testing.T) {
 	if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
 		t.Fatalf("decode: %v", err)
 	}
-	if resp.Queued != h.coverArtBackfillCap {
+	if !resp.Started {
-		t.Errorf("queued = %d, want %d (cap)", resp.Queued, h.coverArtBackfillCap)
+		t.Errorf("started = false, want true (bulk refetch should acknowledge)")
 	}
 }
 

internal/api/api.go

@@ -28,26 +28,25 @@ import (
 // Mount attaches /api/* handlers to r. Public endpoints (login) are outside
 // RequireUser; everything else is gated by the middleware. The events writer
 // is shared with the Subsonic mount so /rest/scrobble feeds the same store.
-func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playevents.Writer, recCfg config.RecommendationConfig, lidarrCfg *lidarrconfig.Service, lidarrReqs *lidarrrequests.Service, lidarrQuar *lidarrquarantine.Service, tracksSvc *tracks.Service, playlistsSvc *playlists.Service, coverEnricher *coverart.Enricher, coverBackfillCap int, coverSettings *coverart.SettingsService, scanner *library.Scanner, scanCfg library.RunScanConfig, scheduler *library.Scheduler, dataDir string, sender mailer.Sender, bus *eventbus.Bus, playlistScheduler *playlists.Scheduler) {
+func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playevents.Writer, recCfg config.RecommendationConfig, lidarrCfg *lidarrconfig.Service, lidarrReqs *lidarrrequests.Service, lidarrQuar *lidarrquarantine.Service, tracksSvc *tracks.Service, playlistsSvc *playlists.Service, coverEnricher *coverart.Enricher, coverSettings *coverart.SettingsService, scanner *library.Scanner, scanCfg library.RunScanConfig, scheduler *library.Scheduler, dataDir string, sender mailer.Sender, bus *eventbus.Bus, playlistScheduler *playlists.Scheduler) {
 	rng := rand.New(rand.NewSource(rand.Int63()))
 	h := &handlers{
 		pool: pool, logger: logger, events: events, recCfg: recCfg,
-		rng:                 rng.Float64,
+		rng:               rng.Float64,
-		lidarrCfg:           lidarrCfg,
+		lidarrCfg:         lidarrCfg,
-		lidarrRequests:      lidarrReqs,
+		lidarrRequests:    lidarrReqs,
-		lidarrQuarantine:    lidarrQuar,
+		lidarrQuarantine:  lidarrQuar,
-		tracks:              tracksSvc,
+		tracks:            tracksSvc,
-		playlists:           playlistsSvc,
+		playlists:         playlistsSvc,
-		coverart:            coverEnricher,
+		coverart:          coverEnricher,
-		coverArtBackfillCap: coverBackfillCap,
+		coverSettings:     coverSettings,
-		coverSettings:       coverSettings,
+		scanner:           scanner,
-		scanner:             scanner,
+		scanCfg:           scanCfg,
-		scanCfg:             scanCfg,
+		scheduler:         scheduler,
-		scheduler:           scheduler,
+		dataDir:           dataDir,
-		dataDir:             dataDir,
+		mailer:            sender,
-		mailer:              sender,
+		eventbus:          bus,
-		eventbus:            bus,
+		playlistScheduler: playlistScheduler,
-		playlistScheduler:   playlistScheduler,
 	}
 
 	r.Route("/api", func(api chi.Router) {
@@ -180,24 +179,23 @@ func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playev
 }
 
 type handlers struct {
-	pool                *pgxpool.Pool
+	pool              *pgxpool.Pool
-	logger              *slog.Logger
+	logger            *slog.Logger
-	events              *playevents.Writer
+	events            *playevents.Writer
-	recCfg              config.RecommendationConfig
+	recCfg            config.RecommendationConfig
-	rng                 func() float64
+	rng               func() float64
-	lidarrCfg           *lidarrconfig.Service
+	lidarrCfg         *lidarrconfig.Service
-	lidarrRequests      *lidarrrequests.Service
+	lidarrRequests    *lidarrrequests.Service
-	lidarrQuarantine    *lidarrquarantine.Service
+	lidarrQuarantine  *lidarrquarantine.Service
-	tracks              *tracks.Service
+	tracks            *tracks.Service
-	playlists           *playlists.Service
+	playlists         *playlists.Service
-	coverart            *coverart.Enricher
+	coverart          *coverart.Enricher
-	coverArtBackfillCap int
+	coverSettings     *coverart.SettingsService
-	coverSettings       *coverart.SettingsService
+	scanner           *library.Scanner
-	scanner             *library.Scanner
+	scanCfg           library.RunScanConfig
-	scanCfg             library.RunScanConfig
+	scheduler         *library.Scheduler
-	scheduler           *library.Scheduler
+	dataDir           string
-	dataDir             string
+	mailer            mailer.Sender
-	mailer              mailer.Sender
+	eventbus          *eventbus.Bus
-	eventbus            *eventbus.Bus
+	playlistScheduler *playlists.Scheduler
-	playlistScheduler   *playlists.Scheduler
 }

internal/api/library_test.go

@@ -444,7 +444,7 @@ func TestRoutesRegisteredInMount(t *testing.T) {
 	r := chi.NewRouter()
 	w := playevents.NewWriter(h.pool, slog.New(slog.NewTextHandler(io.Discard, nil)),
 		30*time.Minute, 0.5, 30000)
-	Mount(r, h.pool, h.logger, w, config.RecommendationConfig{RadioSize: 50, RadioSizeMax: 200, RecentlyPlayedHours: 1}, h.lidarrCfg, h.lidarrRequests, h.lidarrQuarantine, h.tracks, h.playlists, h.coverart, h.coverArtBackfillCap, h.coverSettings, h.scanner, h.scanCfg, nil, h.dataDir, nil, eventbus.New(), nil)
+	Mount(r, h.pool, h.logger, w, config.RecommendationConfig{RadioSize: 50, RadioSizeMax: 200, RecentlyPlayedHours: 1}, h.lidarrCfg, h.lidarrRequests, h.lidarrQuarantine, h.tracks, h.playlists, h.coverart, h.coverSettings, h.scanner, h.scanCfg, nil, h.dataDir, nil, eventbus.New(), nil)
 
 	paths := []string{
 		"/api/artists",

internal/config/config.go

@@ -56,11 +56,10 @@ type LogConfig struct {
 }
 
 type LibraryConfig struct {
-	ScanPaths           []string `yaml:"scan_paths"`
+	ScanPaths         []string `yaml:"scan_paths"`
-	ScanOnStartup       bool     `yaml:"scan_on_startup"`
+	ScanOnStartup     bool     `yaml:"scan_on_startup"`
-	CoverArtFromMBCAA   bool     `yaml:"coverart_from_mbcaa"`   // default true
+	CoverArtFromMBCAA bool     `yaml:"coverart_from_mbcaa"` // default true
-	CoverArtBackfillCap int      `yaml:"coverart_backfill_cap"` // default 500
+	ContactEmail      string   `yaml:"contact_email"`       // optional override for MBCAA UA
-	ContactEmail        string   `yaml:"contact_email"`         // optional override for MBCAA UA
 }
 
 // SubsonicConfig controls wire-format concessions on the /rest/* surface.
@@ -120,8 +119,7 @@ func Default() Config {
 			RadioSizeMax:        200,
 		},
 		Library: LibraryConfig{
-			CoverArtFromMBCAA:   true,
+			CoverArtFromMBCAA: true,
-			CoverArtBackfillCap: 500,
 		},
 	}
 }
@@ -177,11 +175,6 @@ func applyEnv(cfg *Config) {
 			cfg.Library.CoverArtFromMBCAA = b
 		}
 	}
-	if v, ok := os.LookupEnv("MINSTREL_LIBRARY_COVERART_BACKFILL_CAP"); ok {
-		if n, err := strconv.Atoi(v); err == nil {
-			cfg.Library.CoverArtBackfillCap = n
-		}
-	}
 	if v, ok := os.LookupEnv("MINSTREL_CONTACT_EMAIL"); ok {
 		cfg.Library.ContactEmail = v
 	}

internal/coverart/artist_enricher.go

@@ -144,15 +144,21 @@ func (e *Enricher) recordArtistArt(ctx context.Context, artistID pgtype.UUID, th
 // errored). The JSON tally written to scan_runs keeps the existing
 // processed/succeeded/failed shape for backwards compat with the
 // admin overview UI; the log line is the operator's diagnostic.
+// limit: 0 = stage disabled; >0 = bounded; <0 = unbounded (#388 —
+// no global cap; remote providers self-throttle per provider).
 func (e *Enricher) EnrichArtistBatch(ctx context.Context, limit int, dataDir string,
 	progressCb func(processed, succeeded, failed int)) (processed, succeeded, failed int, err error) {
-	if limit <= 0 {
+	if limit == 0 {
 		return 0, 0, 0, nil
 	}
+	queryLimit := int32(limit)
+	if limit < 0 {
+		queryLimit = 1<<31 - 1 // unbounded
+	}
 	q := dbq.New(e.pool)
 	rows, qerr := q.ListArtistsMissingArt(ctx, dbq.ListArtistsMissingArtParams{
 		ArtistArtSourcesVersion: e.settings.CurrentVersion(),
-		Limit:                   int32(limit),
+		Limit:                   queryLimit,
 	})
 	if qerr != nil {
 		return 0, 0, 0, fmt.Errorf("list missing artist art: %w", qerr)

internal/coverart/enricher.go

@@ -213,15 +213,23 @@ func (e *Enricher) recordAlbumCover(ctx context.Context, albumID pgtype.UUID, pa
 // JSON tally written to scan_runs keeps the existing
 // processed/succeeded/failed shape for backwards compat with the
 // admin overview UI; the log line is the operator's diagnostic.
+// limit semantics: 0 = stage disabled (skip); >0 = bounded batch;
+// <0 = unbounded — walk every album needing art. The global cap was
+// removed (#388); external providers self-throttle via their
+// per-provider httpClient MinInterval, local sources run at disk speed.
 func (e *Enricher) EnrichBatch(ctx context.Context, limit int,
 	progressCb func(processed, succeeded, failed int)) (processed, succeeded, failed int, err error) {
-	if limit <= 0 {
+	if limit == 0 {
 		return 0, 0, 0, nil
 	}
+	queryLimit := int32(limit)
+	if limit < 0 {
+		queryLimit = 1<<31 - 1 // unbounded
+	}
 	q := dbq.New(e.pool)
 	rows, qerr := q.ListAlbumsMissingCover(ctx, dbq.ListAlbumsMissingCoverParams{
 		CoverArtSourcesVersion: e.settings.CurrentVersion(),
-		Limit:                  int32(limit),
+		Limit:                  queryLimit,
 	})
 	if qerr != nil {
 		return 0, 0, 0, fmt.Errorf("list missing: %w", qerr)
@@ -293,12 +301,18 @@ func (e *Enricher) logBatchSummary(stage string, eligible, processed, succeeded,
 // EnrichRetryMissing drains both NULL and 'none' rows. Used by the
 // admin bulk-retry endpoint. Clears 'none' to NULL first so
 // EnrichAlbum picks them up.
+// limit: 0 = no-op; >0 = bounded; <0 = unbounded (retry every
+// missing/none album). Admin bulk-retry passes <0 post-#388.
 func (e *Enricher) EnrichRetryMissing(ctx context.Context, limit int) (int, error) {
-	if limit <= 0 {
+	if limit == 0 {
 		return 0, nil
 	}
+	queryLimit := int32(limit)
+	if limit < 0 {
+		queryLimit = 1<<31 - 1 // unbounded
+	}
 	q := dbq.New(e.pool)
-	rows, err := q.ListAlbumsRetryMissing(ctx, int32(limit))
+	rows, err := q.ListAlbumsRetryMissing(ctx, queryLimit)
 	if err != nil {
 		return 0, fmt.Errorf("list retry missing: %w", err)
 	}

internal/db/dbq/system_mixes.sql.go

@@ -202,8 +202,8 @@ WITH windowed AS (
     SELECT track_id, COUNT(*) AS c
       FROM play_events
      WHERE user_id = $1 AND was_skipped = false
-       AND started_at < now() - interval '60 days'
+       AND started_at < now() - interval '30 days'
-       AND ABS(EXTRACT(DOY FROM started_at) - EXTRACT(DOY FROM now())) <= 7
+       AND ABS(EXTRACT(DOY FROM started_at) - EXTRACT(DOY FROM now())) <= 10
      GROUP BY track_id
 )
 SELECT t.id, t.album_id, t.artist_id
@@ -229,9 +229,12 @@ type ListOnThisDayTracksRow struct {
 }
 
 // #422 On This Day: tracks the user played around this calendar date
-// (±7 day-of-year) in the past, excluding the very recent (>60 days
+// (±10 day-of-year) in the past, excluding the very recent (>30 days
 // ago) so it's nostalgic, not just "last week". Weighted by how much
-// they were played in those windows.
+// they were played in those windows. Floor relaxed from 60→30 days
+// and window ±7→±10 so it surfaces on a months-old library instead
+// of needing a full year of history; still skips cleanly (no rows →
+// no playlist) when there's no qualifying history yet.
 // $1 user_id, $2 date string.
 func (q *Queries) ListOnThisDayTracks(ctx context.Context, arg ListOnThisDayTracksParams) ([]ListOnThisDayTracksRow, error) {
 	rows, err := q.db.Query(ctx, listOnThisDayTracks, arg.UserID, arg.Column2)
@@ -255,21 +258,41 @@ func (q *Queries) ListOnThisDayTracks(ctx context.Context, arg ListOnThisDayTrac
 
 const listRediscoverTracks = `-- name: ListRediscoverTracks :many
 WITH stats AS (
-    SELECT track_id, COUNT(*) AS c, MAX(started_at) AS last_at
+    SELECT pe.track_id, COUNT(*) AS c, MAX(pe.started_at) AS last_at
-      FROM play_events
+      FROM play_events pe
-     WHERE user_id = $1 AND was_skipped = false
+     WHERE pe.user_id = $1 AND pe.was_skipped = false
-     GROUP BY track_id
+     GROUP BY pe.track_id
+),
+deep AS (
+    SELECT t.id, t.album_id, t.artist_id, s.c, 0 AS tier
+      FROM tracks t
+      JOIN stats s ON s.track_id = t.id
+     WHERE s.c >= 5
+       AND s.last_at <= now() - interval '6 months'
+       AND NOT EXISTS (
+           SELECT 1 FROM lidarr_quarantine q
+            WHERE q.user_id = $1 AND q.track_id = t.id
+       )
+),
+shallow AS (
+    SELECT t.id, t.album_id, t.artist_id, s.c, 1 AS tier
+      FROM tracks t
+      JOIN stats s ON s.track_id = t.id
+     WHERE s.c >= 5
+       AND s.last_at <= now() - interval '30 days'
+       AND NOT EXISTS (
+           SELECT 1 FROM lidarr_quarantine q
+            WHERE q.user_id = $1 AND q.track_id = t.id
+       )
 )
-SELECT t.id, t.album_id, t.artist_id
+SELECT id, album_id, artist_id
-  FROM tracks t
+  FROM (
-  JOIN stats s ON s.track_id = t.id
+    SELECT id, album_id, artist_id, c, tier FROM deep
- WHERE s.c >= 5
+    UNION ALL
-   AND s.last_at <= now() - interval '6 months'
+    SELECT id, album_id, artist_id, c, tier FROM shallow
-   AND NOT EXISTS (
+     WHERE NOT EXISTS (SELECT 1 FROM deep)
-       SELECT 1 FROM lidarr_quarantine q
+  ) u
-        WHERE q.user_id = $1 AND q.track_id = t.id
+ ORDER BY tier, c DESC, id
-   )
- ORDER BY s.c DESC, t.id
  LIMIT 200
 `
 
@@ -280,8 +303,12 @@ type ListRediscoverTracksRow struct {
 }
 
 // #420 Rediscover: tracks the user played a lot (>=5 non-skip) but
-// not in the last 6 months. Ordered by historical affection.
+// has drifted away from. Tiered so a young library still gets a mix:
-// $1 user_id.
+//
+//	tier 0  not played in the last 6 months (true rediscovery)
+//	tier 1  (only if tier 0 empty) not played in the last 30 days
+//
+// Ordered by historical affection. $1 user_id.
 func (q *Queries) ListRediscoverTracks(ctx context.Context, userID pgtype.UUID) ([]ListRediscoverTracksRow, error) {
 	rows, err := q.db.Query(ctx, listRediscoverTracks, userID)
 	if err != nil {

internal/db/dbq/system_playlists.sql.go

@@ -412,23 +412,55 @@ func (q *Queries) PickTopPlayedTrackForArtistByUser(ctx context.Context, arg Pic
 }
 
 const pickTopPlayedTracksForUser = `-- name: PickTopPlayedTracksForUser :many
-SELECT t.id
+WITH recent AS (
-  FROM play_events pe
+    SELECT t.id, COUNT(*) AS c, 0 AS tier
-  JOIN tracks t ON t.id = pe.track_id
+      FROM play_events pe
- WHERE pe.user_id = $1
+      JOIN tracks t ON t.id = pe.track_id
-   AND pe.started_at > now() - INTERVAL '7 days'
+     WHERE pe.user_id = $1
-   AND pe.was_skipped = false
+       AND pe.started_at > now() - INTERVAL '30 days'
- GROUP BY t.id
+       AND pe.was_skipped = false
- ORDER BY COUNT(*) DESC, t.id
+     GROUP BY t.id
+),
+alltime AS (
+    SELECT t.id, COUNT(*) AS c, 1 AS tier
+      FROM play_events pe
+      JOIN tracks t ON t.id = pe.track_id
+     WHERE pe.user_id = $1
+       AND pe.was_skipped = false
+     GROUP BY t.id
+),
+liked AS (
+    SELECT gl.track_id AS id, 0::bigint AS c, 2 AS tier
+      FROM general_likes gl
+     WHERE gl.user_id = $1
+),
+chosen AS (
+    SELECT id, c, tier FROM recent
+    UNION ALL
+    SELECT id, c, tier FROM alltime
+     WHERE NOT EXISTS (SELECT 1 FROM recent)
+    UNION ALL
+    SELECT id, c, tier FROM liked
+     WHERE NOT EXISTS (SELECT 1 FROM recent)
+       AND NOT EXISTS (SELECT 1 FROM alltime)
+)
+SELECT id
+  FROM chosen
+ ORDER BY tier, c DESC, id
  LIMIT 5
 `
 
-// For-You candidate seeds. Returns the user's top-5 most-played
+// For-You candidate seeds, tiered so For-You never silently vanishes:
-// non-skipped tracks in the last 7 days; tie-break by track_id for
+//
-// determinism. The Go-side picker (pickForYouSeedForDay) chooses one
+//	tier 0  top non-skip plays in the last 30 days
-// of the returned rows as today's seed via userIDHash so the
+//	tier 1  (only if tier 0 empty) all-time top non-skip plays
-// candidate pool rotates day-to-day while staying stable within a
+//	tier 2  (only if tiers 0+1 empty) liked tracks
-// day.
+//
+// Returns up to 5 ids; tie-break by track_id for determinism. The
+// Go-side picker (pickForYouSeedForDay) rotates one per day via
+// userIDHash. Widened from a hard 7-day window, which made For-You
+// disappear after a week of not listening and never recover on a
+// self-hosted library with sparse history.
 func (q *Queries) PickTopPlayedTracksForUser(ctx context.Context, userID pgtype.UUID) ([]pgtype.UUID, error) {
 	rows, err := q.db.Query(ctx, pickTopPlayedTracksForUser, userID)
 	if err != nil {

internal/db/dbq/tracks.sql.go

@@ -376,6 +376,41 @@ func (q *Queries) ListTracksByAlbum(ctx context.Context, arg ListTracksByAlbumPa
 	return items, nil
 }
 
+const listTracksMissingMbidWithPath = `-- name: ListTracksMissingMbidWithPath :many
+SELECT id, file_path
+  FROM tracks
+ WHERE mbid IS NULL
+ ORDER BY id
+ LIMIT $1
+`
+
+type ListTracksMissingMbidWithPathRow struct {
+	ID       pgtype.UUID
+	FilePath string
+}
+
+// Track recording-MBID backfill: tracks with NULL mbid that still have
+// a file to re-read. $1 caps the batch (mirrors the album backfill).
+func (q *Queries) ListTracksMissingMbidWithPath(ctx context.Context, limit int32) ([]ListTracksMissingMbidWithPathRow, error) {
+	rows, err := q.db.Query(ctx, listTracksMissingMbidWithPath, limit)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []ListTracksMissingMbidWithPathRow
+	for rows.Next() {
+		var i ListTracksMissingMbidWithPathRow
+		if err := rows.Scan(&i.ID, &i.FilePath); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
 const searchTracks = `-- name: SearchTracks :many
 SELECT id, title, album_id, artist_id, track_number, disc_number, duration_ms, file_path, file_size, file_format, bitrate, mbid, genre, added_at, updated_at FROM tracks
 WHERE title ILIKE '%' || $1::text || '%'
@@ -437,6 +472,24 @@ func (q *Queries) SearchTracks(ctx context.Context, arg SearchTracksParams) ([]T
 	return items, nil
 }
 
+const setTrackMbidIfNull = `-- name: SetTrackMbidIfNull :exec
+UPDATE tracks
+   SET mbid = $2, updated_at = now()
+ WHERE id = $1 AND mbid IS NULL
+`
+
+type SetTrackMbidIfNullParams struct {
+	ID   pgtype.UUID
+	Mbid *string
+}
+
+// Heal a track's recording MBID only while still NULL — idempotent, so
+// re-running the backfill is a no-op for already-healed rows.
+func (q *Queries) SetTrackMbidIfNull(ctx context.Context, arg SetTrackMbidIfNullParams) error {
+	_, err := q.db.Exec(ctx, setTrackMbidIfNull, arg.ID, arg.Mbid)
+	return err
+}
+
 const upsertTrack = `-- name: UpsertTrack :one
 INSERT INTO tracks (
     title, album_id, artist_id, track_number, disc_number,

internal/db/migrations/0028_discovery_mix_variants.down.sql

@@ -0,0 +1,24 @@
+-- Reverts to the 0021 constraint set (for_you, songs_like_artist,
+-- discover only). Fails if any playlists row still has one of the
+-- five new system_variant values — delete/rebuild system playlists
+-- first if rolling back.
+
+ALTER TABLE playlists DROP CONSTRAINT IF EXISTS playlists_kind_variant_consistent;
+ALTER TABLE playlists
+    ADD CONSTRAINT playlists_kind_variant_consistent CHECK (
+        (kind = 'user'   AND system_variant IS NULL)
+        OR
+        (kind = 'system' AND system_variant IN ('for_you', 'songs_like_artist', 'discover'))
+    );
+
+ALTER TABLE playlists DROP CONSTRAINT IF EXISTS playlists_seed_consistent;
+ALTER TABLE playlists
+    ADD CONSTRAINT playlists_seed_consistent CHECK (
+        (system_variant IS NULL                 AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'for_you'             AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'discover'            AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'songs_like_artist'   AND seed_artist_id IS NOT NULL)
+    );

internal/db/migrations/0028_discovery_mix_variants.up.sql

@@ -0,0 +1,47 @@
+-- #411 R3 bugfix: the five discovery mixes (deep_cuts, rediscover,
+-- new_for_you, on_this_day, first_listens) were added as producers +
+-- registry entries but their system_variant values were never added
+-- to the two playlists CHECK constraints. Result: insertSystemPlaylist
+-- for any new mix fails with playlists_kind_variant_consistent
+-- (SQLSTATE 23514), which — because BuildSystemPlaylists is one
+-- all-or-nothing transaction — aborts the WHOLE build, so For-You /
+-- Discover refresh 500s and the lazy daily build fails too.
+--
+-- All five are seedless (like for_you/discover): seed_artist_id IS
+-- NULL. Drop + re-add both constraints with the expanded set, same
+-- pattern as 0021_discover_variant (Postgres has no ALTER CONSTRAINT
+-- for CHECK).
+
+ALTER TABLE playlists DROP CONSTRAINT IF EXISTS playlists_kind_variant_consistent;
+ALTER TABLE playlists
+    ADD CONSTRAINT playlists_kind_variant_consistent CHECK (
+        (kind = 'user'   AND system_variant IS NULL)
+        OR
+        (kind = 'system' AND system_variant IN (
+            'for_you', 'songs_like_artist', 'discover',
+            'deep_cuts', 'rediscover', 'new_for_you',
+            'on_this_day', 'first_listens'
+        ))
+    );
+
+ALTER TABLE playlists DROP CONSTRAINT IF EXISTS playlists_seed_consistent;
+ALTER TABLE playlists
+    ADD CONSTRAINT playlists_seed_consistent CHECK (
+        (system_variant IS NULL                 AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'for_you'             AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'discover'            AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'deep_cuts'           AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'rediscover'          AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'new_for_you'         AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'on_this_day'         AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'first_listens'       AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'songs_like_artist'   AND seed_artist_id IS NOT NULL)
+    );

internal/db/migrations/0029_tracks_mbid_nonunique.down.sql

@@ -0,0 +1,6 @@
+-- Reverts to the unique partial index. This FAILS if any recording
+-- MBID is shared across releases in the library (the exact case 0029
+-- exists to allow) — dedupe tracks.mbid before rolling back.
+
+DROP INDEX IF EXISTS tracks_mbid_idx;
+CREATE UNIQUE INDEX tracks_mbid_unique ON tracks (mbid) WHERE mbid IS NOT NULL;

internal/db/migrations/0029_tracks_mbid_nonunique.up.sql

@@ -0,0 +1,15 @@
+-- tracks.mbid holds the MusicBrainz *recording* MBID — the id the
+-- ListenBrainz similarity pipeline (ListPlayedTracksNeedingSimilarity,
+-- GetTracksByMBIDs) matches on. A single recording legitimately appears
+-- on multiple releases (album + compilation + single), so multiple
+-- tracks rows share one recording MBID.
+--
+-- tracks_mbid_unique (added in 0002, when this column was always NULL
+-- and never populated) wrongly assumes one MBID == one track. Now that
+-- the scanner extracts the recording MBID, that uniqueness throws
+-- 23505 for any recording present on >1 release. Replace it with a
+-- non-unique partial index serving the same lookups. Zero-risk: the
+-- column is 100% NULL at migration time.
+
+DROP INDEX IF EXISTS tracks_mbid_unique;
+CREATE INDEX IF NOT EXISTS tracks_mbid_idx ON tracks (mbid) WHERE mbid IS NOT NULL;

internal/db/queries/system_mixes.sql

@@ -38,24 +38,46 @@ SELECT t.id, t.album_id, t.artist_id
 
 -- name: ListRediscoverTracks :many
 -- #420 Rediscover: tracks the user played a lot (>=5 non-skip) but
--- not in the last 6 months. Ordered by historical affection.
+-- has drifted away from. Tiered so a young library still gets a mix:
--- $1 user_id.
+--   tier 0  not played in the last 6 months (true rediscovery)
+--   tier 1  (only if tier 0 empty) not played in the last 30 days
+-- Ordered by historical affection. $1 user_id.
 WITH stats AS (
-    SELECT track_id, COUNT(*) AS c, MAX(started_at) AS last_at
+    SELECT pe.track_id, COUNT(*) AS c, MAX(pe.started_at) AS last_at
-      FROM play_events
+      FROM play_events pe
-     WHERE user_id = $1 AND was_skipped = false
+     WHERE pe.user_id = $1 AND pe.was_skipped = false
-     GROUP BY track_id
+     GROUP BY pe.track_id
+),
+deep AS (
+    SELECT t.id, t.album_id, t.artist_id, s.c, 0 AS tier
+      FROM tracks t
+      JOIN stats s ON s.track_id = t.id
+     WHERE s.c >= 5
+       AND s.last_at <= now() - interval '6 months'
+       AND NOT EXISTS (
+           SELECT 1 FROM lidarr_quarantine q
+            WHERE q.user_id = $1 AND q.track_id = t.id
+       )
+),
+shallow AS (
+    SELECT t.id, t.album_id, t.artist_id, s.c, 1 AS tier
+      FROM tracks t
+      JOIN stats s ON s.track_id = t.id
+     WHERE s.c >= 5
+       AND s.last_at <= now() - interval '30 days'
+       AND NOT EXISTS (
+           SELECT 1 FROM lidarr_quarantine q
+            WHERE q.user_id = $1 AND q.track_id = t.id
+       )
 )
-SELECT t.id, t.album_id, t.artist_id
+SELECT id, album_id, artist_id
-  FROM tracks t
+  FROM (
-  JOIN stats s ON s.track_id = t.id
+    SELECT id, album_id, artist_id, c, tier FROM deep
- WHERE s.c >= 5
+    UNION ALL
-   AND s.last_at <= now() - interval '6 months'
+    SELECT id, album_id, artist_id, c, tier FROM shallow
-   AND NOT EXISTS (
+     WHERE NOT EXISTS (SELECT 1 FROM deep)
-       SELECT 1 FROM lidarr_quarantine q
+  ) u
-        WHERE q.user_id = $1 AND q.track_id = t.id
+ ORDER BY tier, c DESC, id
-   )
- ORDER BY s.c DESC, t.id
  LIMIT 200;
 
 -- name: ListNewForYouTracks :many
@@ -87,16 +109,19 @@ SELECT t.id, t.album_id, t.artist_id
 
 -- name: ListOnThisDayTracks :many
 -- #422 On This Day: tracks the user played around this calendar date
--- (±7 day-of-year) in the past, excluding the very recent (>60 days
+-- (±10 day-of-year) in the past, excluding the very recent (>30 days
 -- ago) so it's nostalgic, not just "last week". Weighted by how much
--- they were played in those windows.
+-- they were played in those windows. Floor relaxed from 60→30 days
+-- and window ±7→±10 so it surfaces on a months-old library instead
+-- of needing a full year of history; still skips cleanly (no rows →
+-- no playlist) when there's no qualifying history yet.
 -- $1 user_id, $2 date string.
 WITH windowed AS (
     SELECT track_id, COUNT(*) AS c
       FROM play_events
      WHERE user_id = $1 AND was_skipped = false
-       AND started_at < now() - interval '60 days'
+       AND started_at < now() - interval '30 days'
-       AND ABS(EXTRACT(DOY FROM started_at) - EXTRACT(DOY FROM now())) <= 7
+       AND ABS(EXTRACT(DOY FROM started_at) - EXTRACT(DOY FROM now())) <= 10
      GROUP BY track_id
 )
 SELECT t.id, t.album_id, t.artist_id

internal/db/queries/system_playlists.sql

@@ -73,20 +73,50 @@ SELECT p.artist_id,
  LIMIT 5;
 
 -- name: PickTopPlayedTracksForUser :many
--- For-You candidate seeds. Returns the user's top-5 most-played
+-- For-You candidate seeds, tiered so For-You never silently vanishes:
--- non-skipped tracks in the last 7 days; tie-break by track_id for
+--   tier 0  top non-skip plays in the last 30 days
--- determinism. The Go-side picker (pickForYouSeedForDay) chooses one
+--   tier 1  (only if tier 0 empty) all-time top non-skip plays
--- of the returned rows as today's seed via userIDHash so the
+--   tier 2  (only if tiers 0+1 empty) liked tracks
--- candidate pool rotates day-to-day while staying stable within a
+-- Returns up to 5 ids; tie-break by track_id for determinism. The
--- day.
+-- Go-side picker (pickForYouSeedForDay) rotates one per day via
-SELECT t.id
+-- userIDHash. Widened from a hard 7-day window, which made For-You
-  FROM play_events pe
+-- disappear after a week of not listening and never recover on a
-  JOIN tracks t ON t.id = pe.track_id
+-- self-hosted library with sparse history.
- WHERE pe.user_id = $1
+WITH recent AS (
-   AND pe.started_at > now() - INTERVAL '7 days'
+    SELECT t.id, COUNT(*) AS c, 0 AS tier
-   AND pe.was_skipped = false
+      FROM play_events pe
- GROUP BY t.id
+      JOIN tracks t ON t.id = pe.track_id
- ORDER BY COUNT(*) DESC, t.id
+     WHERE pe.user_id = $1
+       AND pe.started_at > now() - INTERVAL '30 days'
+       AND pe.was_skipped = false
+     GROUP BY t.id
+),
+alltime AS (
+    SELECT t.id, COUNT(*) AS c, 1 AS tier
+      FROM play_events pe
+      JOIN tracks t ON t.id = pe.track_id
+     WHERE pe.user_id = $1
+       AND pe.was_skipped = false
+     GROUP BY t.id
+),
+liked AS (
+    SELECT gl.track_id AS id, 0::bigint AS c, 2 AS tier
+      FROM general_likes gl
+     WHERE gl.user_id = $1
+),
+chosen AS (
+    SELECT id, c, tier FROM recent
+    UNION ALL
+    SELECT id, c, tier FROM alltime
+     WHERE NOT EXISTS (SELECT 1 FROM recent)
+    UNION ALL
+    SELECT id, c, tier FROM liked
+     WHERE NOT EXISTS (SELECT 1 FROM recent)
+       AND NOT EXISTS (SELECT 1 FROM alltime)
+)
+SELECT id
+  FROM chosen
+ ORDER BY tier, c DESC, id
  LIMIT 5;
 
 -- name: PickTopPlayedTrackForArtistByUser :one

internal/db/queries/tracks.sql

@@ -19,6 +19,22 @@ ON CONFLICT (file_path) DO UPDATE SET
     updated_at = now()
 RETURNING *;
 
+-- name: ListTracksMissingMbidWithPath :many
+-- Track recording-MBID backfill: tracks with NULL mbid that still have
+-- a file to re-read. $1 caps the batch (mirrors the album backfill).
+SELECT id, file_path
+  FROM tracks
+ WHERE mbid IS NULL
+ ORDER BY id
+ LIMIT $1;
+
+-- name: SetTrackMbidIfNull :exec
+-- Heal a track's recording MBID only while still NULL — idempotent, so
+-- re-running the backfill is a no-op for already-healed rows.
+UPDATE tracks
+   SET mbid = $2, updated_at = now()
+ WHERE id = $1 AND mbid IS NULL;
+
 -- name: GetTrackByID :one
 SELECT * FROM tracks WHERE id = $1;
 

internal/library/mbidbackfill.go

@@ -167,3 +167,96 @@ func readMBIDsForFile(path string, logger *slog.Logger) (albumMBID, artistMBID s
 	}
 	return extractMBIDs(meta)
 }
+
+// BackfillTrackMBIDsResult tallies the track recording-MBID backfill.
+type BackfillTrackMBIDsResult struct {
+	Processed int // Tracks considered (mbid IS NULL).
+	Healed    int // Tracks whose recording MBID we set.
+	Skipped   int // Tracks whose file was missing / untagged / write failed.
+}
+
+// BackfillTrackMBIDs walks tracks with NULL mbid, re-reads each file's
+// tags, and persists the MusicBrainz recording MBID. This is the
+// counterpart to BackfillMBIDs (which heals album/artist MBIDs); it
+// unblocks the ListenBrainz similarity pipeline, which is gated on
+// tracks.mbid IS NOT NULL.
+//
+// Idempotent via SetTrackMbidIfNull: re-running costs the same N file
+// reads but is a no-op for already-healed rows. limit caps one call;
+// pass -1 for unbounded (caller normally batches per scan).
+func BackfillTrackMBIDs(ctx context.Context, pool *pgxpool.Pool, logger *slog.Logger,
+	limit int, progressCb func(BackfillTrackMBIDsResult)) (BackfillTrackMBIDsResult, error) {
+	q := dbq.New(pool)
+	queryLimit := int32(limit)
+	if limit < 0 {
+		queryLimit = 1<<31 - 1 // effectively unbounded
+	}
+
+	rows, err := q.ListTracksMissingMbidWithPath(ctx, queryLimit)
+	if err != nil {
+		return BackfillTrackMBIDsResult{}, fmt.Errorf("list tracks missing mbid: %w", err)
+	}
+
+	var res BackfillTrackMBIDsResult
+	for i, r := range rows {
+		if ctx.Err() != nil {
+			return res, ctx.Err()
+		}
+		res.Processed++
+
+		rec := readRecordingMBIDForFile(r.FilePath, logger)
+		if rec == "" {
+			res.Skipped++
+			if progressCb != nil {
+				progressCb(res)
+			}
+			continue
+		}
+
+		m := rec
+		if uerr := q.SetTrackMbidIfNull(ctx, dbq.SetTrackMbidIfNullParams{
+			ID: r.ID, Mbid: &m,
+		}); uerr != nil {
+			logger.Warn("track mbid backfill: set failed",
+				"track_id", r.ID, "err", uerr)
+			res.Skipped++
+			if progressCb != nil {
+				progressCb(res)
+			}
+			continue
+		}
+
+		res.Healed++
+		if (i+1)%500 == 0 {
+			logger.Info("track mbid backfill progress",
+				"processed", res.Processed, "healed", res.Healed, "skipped", res.Skipped)
+		}
+		if progressCb != nil {
+			progressCb(res)
+		}
+	}
+
+	logger.Info("track mbid backfill complete",
+		"processed", res.Processed, "healed", res.Healed, "skipped", res.Skipped)
+	return res, nil
+}
+
+// readRecordingMBIDForFile opens one audio file and returns its
+// MusicBrainz recording MBID, or "" when the file can't be opened, the
+// tag read fails, or the tag is absent. Errors are logged at Warn, not
+// propagated — one broken file must not halt the backfill.
+func readRecordingMBIDForFile(path string, logger *slog.Logger) string {
+	f, err := os.Open(path)
+	if err != nil {
+		logger.Warn("track mbid backfill: open failed", "path", path, "err", err)
+		return ""
+	}
+	defer func() { _ = f.Close() }()
+
+	meta, err := tag.ReadFrom(f)
+	if err != nil {
+		logger.Warn("track mbid backfill: tag read failed", "path", path, "err", err)
+		return ""
+	}
+	return extractRecordingMBID(meta)
+}

internal/library/mbids.go

@@ -27,6 +27,20 @@ func extractMBIDs(m tag.Metadata) (albumMBID, artistMBID string) {
 	return cleanMBID(info.Get(mbz.Album)), cleanMBID(info.Get(mbz.Artist))
 }
 
+// extractRecordingMBID reads the MusicBrainz *recording* ID — Picard's
+// musicbrainz_recordingid, surfaced by dhowden/tag as mbz.Recording
+// (tag display name "MusicBrainz Track Id"). This is the id the
+// ListenBrainz Labs similar-recordings API keys on and what tracks.mbid
+// stores.
+//
+// Deliberately NOT mbz.Track ("MusicBrainz Release Track Id"): that is
+// per-release-track, whereas similarity is per-recording. Kept separate
+// from extractMBIDs so its existing (album, artist) signature and unit
+// tests stay untouched.
+func extractRecordingMBID(m tag.Metadata) string {
+	return cleanMBID(mbz.Extract(m).Get(mbz.Recording))
+}
+
 func cleanMBID(s string) string {
 	if s == "" {
 		return ""

internal/library/scanner.go

@@ -142,6 +142,7 @@ func (s *Scanner) scanFile(ctx context.Context, q *dbq.Queries, path string, sta
 		return fmt.Errorf("tag read: %w", err)
 	}
 	albumMBID, artistMBID := extractMBIDs(meta)
+	recordingMBID := extractRecordingMBID(meta)
 
 	artistName := meta.Artist()
 	if artistName == "" {
@@ -195,6 +196,13 @@ func (s *Scanner) scanFile(ctx context.Context, q *dbq.Queries, path string, sta
 	if g := meta.Genre(); g != "" {
 		params.Genre = &g
 	}
+	// Recording MBID feeds the ListenBrainz similarity pipeline.
+	// UpsertTrack heals mbid on the file_path conflict, so a re-scan
+	// of a previously-untagged-into-DB track backfills it for free.
+	if recordingMBID != "" {
+		m := recordingMBID
+		params.Mbid = &m
+	}
 
 	track, err := q.UpsertTrack(ctx, params)
 	if err != nil {

internal/library/scanrun.go

@@ -49,9 +49,11 @@ type ArtistArtEnrichStageTallies struct {
 	Failed    int `json:"failed"`
 }
 
-// RunScanConfig assembles the knobs for the orchestrator. BackfillCap and
+// RunScanConfig assembles the knobs for the orchestrator. BackfillCap is
-// EnrichCap mirror the existing boot-time caps (5000 / coverArtBackfillCap)
+// the album/artist-MBID-backfill batch cap (5000); EnrichCap /
-// so manual triggers don't accidentally drain the whole library.
+// ArtistEnrichCap gate cover/artist-art enrichment (0 = off, <0 =
+// unbounded — #388 removed the global cover-art cap; remote providers
+// self-throttle per provider).
 type RunScanConfig struct {
 	BackfillCap     int
 	EnrichCap       int
@@ -154,6 +156,22 @@ func RunScan(
 		}
 	}
 
+	// Stage 2b: track recording-MBID backfill. Unblocks the ListenBrainz
+	// similarity pipeline (gated on tracks.mbid IS NOT NULL). Log-only
+	// progress — no scan_runs jsonb column to avoid a schema addition.
+	//
+	// Unbounded (-1), unlike the album backfill's 5000 staged cap: this
+	// is a one-time whole-library heal with no progress UI, and a cap
+	// just means tracks.mbid stays partially NULL until N future scans
+	// catch up (re-reading untagged files wastefully each pass). One
+	// uncapped pass converges; subsequent scans only re-read the
+	// remaining NULL (genuinely untagged) rows, which is cheap.
+	if cfg.BackfillCap != 0 {
+		if _, tberr := BackfillTrackMBIDs(ctx, pool, logger, -1, nil); tberr != nil {
+			captureErr("track_mbid_backfill", tberr)
+		}
+	}
+
 	// Stage 3: cover enrichment.
 	if enricher != nil && cfg.EnrichCap != 0 {
 		var lastP, lastS, lastF int

internal/playlists/system.go

@@ -289,6 +289,23 @@ var systemPlaylistRegistry = []systemPlaylistKind{
 	{Key: "first_listens", Singleton: true, Produce: produceFirstListens},
 }
 
+// systemForYouSourceLimits is a deeper candidate pool than the radio
+// default. On a self-hosted library without ListenBrainz similarity
+// data the lb_similar / similar_artists sources contribute nothing,
+// so the default (~130 raw, ~40 after dedup + diversity caps) can
+// never fill For-You's 100-track head/tail. The raised random/tag
+// fill keeps For-You ~100 deep regardless of LB enrichment; when LB
+// data IS present the larger lb/similar K just makes it richer.
+func systemForYouSourceLimits() recommendation.CandidateSourceLimits {
+	return recommendation.CandidateSourceLimits{
+		LBSimilar:     80,
+		SimilarArtist: 80,
+		TagOverlap:    60,
+		LikesOverlap:  40,
+		RandomFill:    150,
+	}
+}
+
 // produceForYou: today's seed from the user's top-5 played tracks
 // (rotates daily via userIDHash), similarity candidate pool, head+
 // tail composition. The base seed query failing is fatal; a
@@ -311,7 +328,7 @@ func produceForYou(
 		1, // recentlyPlayedHours — small to avoid filtering the seed's recent neighbourhood
 		zeroVec,
 		[]pgtype.UUID{forYouSeed},
-		recommendation.DefaultCandidateSourceLimits(),
+		systemForYouSourceLimits(),
 	)
 	if cerr != nil {
 		logger.Warn("system playlist: for-you candidates load failed; skipping",

internal/scrobble/listenbrainz/client.go

@@ -17,6 +17,13 @@ import (
 
 const defaultBaseURL = "https://api.listenbrainz.org"
 
+// defaultLabsBaseURL is the ListenBrainz *Labs* API — a DIFFERENT host
+// from the main API. Similarity datasets (similar-recordings /
+// similar-artists) live here, not under api.listenbrainz.org. The old
+// api.listenbrainz.org/1/explore/... paths are website routes, not API
+// endpoints, and 404 for every request.
+const defaultLabsBaseURL = "https://labs.api.listenbrainz.org"
+
 // Listen is one row sent to ListenBrainz.
 type Listen struct {
 	ListenedAt int64 // unix seconds
@@ -35,18 +42,22 @@ type Track struct {
 	ReleaseMBID   string
 }
 
-// Client posts to the LB submit-listens endpoint.
+// Client posts to the LB submit-listens endpoint and queries the Labs
+// API for similarity. BaseURL is the main API; LabsBaseURL is the
+// separate Labs host (see defaultLabsBaseURL).
 type Client struct {
-	BaseURL string
+	BaseURL     string
-	HTTP    *http.Client
+	LabsBaseURL string
+	HTTP        *http.Client
 }
 
-// NewClient returns a default-configured client (LB production base URL,
+// NewClient returns a default-configured client (LB production base
-// 30s timeout).
+// URLs, 30s timeout).
 func NewClient() *Client {
 	return &Client{
-		BaseURL: defaultBaseURL,
+		BaseURL:     defaultBaseURL,
-		HTTP:    &http.Client{Timeout: 30 * time.Second},
+		LabsBaseURL: defaultLabsBaseURL,
+		HTTP:        &http.Client{Timeout: 30 * time.Second},
 	}
 }
 
@@ -181,26 +192,31 @@ func buildPayload(listenType string, listens []Listen) payload {
 	return payload{ListenType: listenType, Payload: entries}
 }
 
-// LB algorithm parameter for /explore/similar-recordings/. Hardcoded for v1
+// lbSimilarRecordingsAlgorithm is a Labs-API-valid algorithm enum (the
-// — matches LB's documented default.
+// value is verified against labs.api.listenbrainz.org; the old
-const lbSimilarRecordingsAlgorithm = "session_based_days_7500_session_30_contribution_5_threshold_15_limit_100_filter_True_skip_30"
+// "_session_30_…_limit_100_filter_True…" string is NOT a permitted
+// member and 400s). limit_50 is baked into the name — there is no
+// separate count/limit query param.
+const lbSimilarRecordingsAlgorithm = "session_based_days_9000_session_300_contribution_5_threshold_15_limit_50_skip_30"
 
-// SimilarRecording is one entry in the /explore/similar-recordings response.
+// SimilarRecording is one entry in the Labs similar-recordings response.
 type SimilarRecording struct {
 	MBID  string  `json:"recording_mbid"`
 	Score float64 `json:"score"`
 }
 
-// SimilarRecordings fetches up to `limit` similar recordings for the given
+// SimilarRecordings fetches similar recordings for the given recording
-// recording MBID. Public endpoint — no token required. Returns the same
+// MBID from the ListenBrainz Labs API. Public endpoint — no token
-// typed errors as SubmitListens.
+// required. The result count is fixed by the algorithm (limit_50); the
-func (c *Client) SimilarRecordings(ctx context.Context, mbid string, limit int) ([]SimilarRecording, error) {
+// caller applies its own top-K. Returns the same typed errors as
-	base := c.BaseURL
+// SubmitListens.
+func (c *Client) SimilarRecordings(ctx context.Context, mbid string, _ int) ([]SimilarRecording, error) {
+	base := c.LabsBaseURL
 	if base == "" {
-		base = defaultBaseURL
+		base = defaultLabsBaseURL
 	}
-	url := fmt.Sprintf("%s/1/explore/similar-recordings/%s?algorithm=%s&count=%d",
+	url := fmt.Sprintf("%s/similar-recordings/json?recording_mbids=%s&algorithm=%s",
-		base, mbid, lbSimilarRecordingsAlgorithm, limit)
+		base, mbid, lbSimilarRecordingsAlgorithm)
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
 	if err != nil {
 		return nil, fmt.Errorf("listenbrainz: build similar-recordings request: %w", err)
@@ -234,29 +250,34 @@ func (c *Client) SimilarRecordings(ctx context.Context, mbid string, limit int)
 	}
 }
 
-// LB algorithm parameter for /explore/similar-artists/. Hardcoded for v1
+// lbSimilarArtistsAlgorithm is a Labs-API-valid algorithm enum (verified
-// — matches LB's documented default.
+// against labs.api.listenbrainz.org; shares the same permitted set as
-const lbSimilarArtistsAlgorithm = "session_based_days_7500_session_30_contribution_5_threshold_15_limit_100_filter_True_skip_30"
+// similar-recordings). The old value 400s. limit_50 is baked in — no
+// separate count/limit query param.
+const lbSimilarArtistsAlgorithm = "session_based_days_9000_session_300_contribution_5_threshold_15_limit_50_skip_30"
 
-// SimilarArtist is one entry in the /explore/similar-artists response.
+// SimilarArtist is one entry in the Labs similar-artists response. Name
-// Name is captured from the LB payload so M5c can render the artist's
+// is captured from the LB payload so M5c can render the artist's name
-// name on out-of-library suggestions without an extra MusicBrainz lookup.
+// on out-of-library suggestions without an extra MusicBrainz lookup.
+// (The Labs payload also carries comment/type/gender/reference_mbid;
+// those are intentionally ignored.)
 type SimilarArtist struct {
 	MBID  string  `json:"artist_mbid"`
 	Name  string  `json:"name"`
 	Score float64 `json:"score"`
 }
 
-// SimilarArtists fetches up to `limit` similar artists for the given
+// SimilarArtists fetches similar artists for the given artist MBID from
-// artist MBID. Public endpoint — no token required. Returns the same
+// the ListenBrainz Labs API. Public endpoint — no token required. The
-// typed errors as SubmitListens.
+// result count is fixed by the algorithm (limit_50); the caller applies
-func (c *Client) SimilarArtists(ctx context.Context, mbid string, limit int) ([]SimilarArtist, error) {
+// its own top-K. Returns the same typed errors as SubmitListens.
-	base := c.BaseURL
+func (c *Client) SimilarArtists(ctx context.Context, mbid string, _ int) ([]SimilarArtist, error) {
+	base := c.LabsBaseURL
 	if base == "" {
-		base = defaultBaseURL
+		base = defaultLabsBaseURL
 	}
-	url := fmt.Sprintf("%s/1/explore/similar-artists/%s?algorithm=%s&count=%d",
+	url := fmt.Sprintf("%s/similar-artists/json?artist_mbids=%s&algorithm=%s",
-		base, mbid, lbSimilarArtistsAlgorithm, limit)
+		base, mbid, lbSimilarArtistsAlgorithm)
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
 	if err != nil {
 		return nil, fmt.Errorf("listenbrainz: build similar-artists request: %w", err)

internal/scrobble/listenbrainz/client_test.go

@@ -12,7 +12,7 @@ import (
 
 func newTestClient(handler http.HandlerFunc) (*Client, *httptest.Server) {
 	srv := httptest.NewServer(handler)
-	return &Client{BaseURL: srv.URL, HTTP: srv.Client()}, srv
+	return &Client{BaseURL: srv.URL, LabsBaseURL: srv.URL, HTTP: srv.Client()}, srv
 }
 
 func TestClient_SubmitListens_Success(t *testing.T) {
@@ -196,7 +196,7 @@ func TestClient_SimilarRecordings_AlgorithmParamSet(t *testing.T) {
 	}
 }
 
-func TestClient_SimilarRecordings_LimitParamSet(t *testing.T) {
+func TestClient_SimilarRecordings_MbidParamSet(t *testing.T) {
 	var seenURL string
 	c, srv := newTestClient(func(w http.ResponseWriter, r *http.Request) {
 		seenURL = r.URL.String()
@@ -204,8 +204,13 @@ func TestClient_SimilarRecordings_LimitParamSet(t *testing.T) {
 	})
 	defer srv.Close()
 	_, _ = c.SimilarRecordings(context.Background(), "abc", 50)
-	if !strings.Contains(seenURL, "count=50") && !strings.Contains(seenURL, "limit=50") {
+	// Labs API takes the MBID as a query param, not a path segment; the
-		t.Errorf("URL missing count/limit param: %q", seenURL)
+	// result count is fixed by the algorithm (no count/limit param).
+	if !strings.Contains(seenURL, "recording_mbids=abc") {
+		t.Errorf("URL missing recording_mbids param: %q", seenURL)
+	}
+	if !strings.Contains(seenURL, "/similar-recordings/json") {
+		t.Errorf("URL not the Labs similar-recordings endpoint: %q", seenURL)
 	}
 }
 
@@ -291,7 +296,7 @@ func TestClient_SimilarArtists_AlgorithmParamSet(t *testing.T) {
 	}
 }
 
-func TestClient_SimilarArtists_LimitParamSet(t *testing.T) {
+func TestClient_SimilarArtists_MbidParamSet(t *testing.T) {
 	var seenURL string
 	c, srv := newTestClient(func(w http.ResponseWriter, r *http.Request) {
 		seenURL = r.URL.String()
@@ -299,8 +304,11 @@ func TestClient_SimilarArtists_LimitParamSet(t *testing.T) {
 	})
 	defer srv.Close()
 	_, _ = c.SimilarArtists(context.Background(), "abc", 50)
-	if !strings.Contains(seenURL, "count=50") && !strings.Contains(seenURL, "limit=50") {
+	if !strings.Contains(seenURL, "artist_mbids=abc") {
-		t.Errorf("URL missing count/limit param: %q", seenURL)
+		t.Errorf("URL missing artist_mbids param: %q", seenURL)
+	}
+	if !strings.Contains(seenURL, "/similar-artists/json") {
+		t.Errorf("URL not the Labs similar-artists endpoint: %q", seenURL)
 	}
 }
 

internal/server/server.go

@@ -72,14 +72,13 @@ type Server struct {
 	// playlist cover collages under <DataDir>/playlist_covers/). Empty
 	// strings are tolerated by tests that don't exercise persisted-cover
 	// codepaths; production callers should pass a writable directory.
-	DataDir             string
+	DataDir        string
-	BrandingCfg         config.BrandingConfig
+	BrandingCfg    config.BrandingConfig
-	CoverEnricher       *coverart.Enricher
+	CoverEnricher  *coverart.Enricher
-	CoverArtBackfillCap int
+	CoverSettings  *coverart.SettingsService
-	CoverSettings       *coverart.SettingsService
+	LibraryScanner *library.Scanner
-	LibraryScanner      *library.Scanner
+	ScanCfg        library.RunScanConfig
-	ScanCfg             library.RunScanConfig
+	Scheduler      *library.Scheduler
-	Scheduler           *library.Scheduler
 	// Bus is the live-event bus shared with background workers (the
 	// lidarr reconciler, scan scheduler) constructed in cmd/minstrel/main.go.
 	// When nil, Router() constructs a local fallback (test contexts).
@@ -92,8 +91,8 @@ type Server struct {
 	PlaylistScheduler *playlists.Scheduler
 }
 
-func New(logger *slog.Logger, pool *pgxpool.Pool, scanner ScanTrigger, subCfg subsonic.Config, eventsCfg config.EventsConfig, recCfg config.RecommendationConfig, dataDir string, brandingCfg config.BrandingConfig, coverEnricher *coverart.Enricher, coverArtBackfillCap int, coverSettings *coverart.SettingsService, libraryScanner *library.Scanner, scanCfg library.RunScanConfig, scheduler *library.Scheduler) *Server {
+func New(logger *slog.Logger, pool *pgxpool.Pool, scanner ScanTrigger, subCfg subsonic.Config, eventsCfg config.EventsConfig, recCfg config.RecommendationConfig, dataDir string, brandingCfg config.BrandingConfig, coverEnricher *coverart.Enricher, coverSettings *coverart.SettingsService, libraryScanner *library.Scanner, scanCfg library.RunScanConfig, scheduler *library.Scheduler) *Server {
-	return &Server{Logger: logger, Pool: pool, Scanner: scanner, SubsonicCfg: subCfg, EventsCfg: eventsCfg, RecommendationCfg: recCfg, DataDir: dataDir, BrandingCfg: brandingCfg, CoverEnricher: coverEnricher, CoverArtBackfillCap: coverArtBackfillCap, CoverSettings: coverSettings, LibraryScanner: libraryScanner, ScanCfg: scanCfg, Scheduler: scheduler}
+	return &Server{Logger: logger, Pool: pool, Scanner: scanner, SubsonicCfg: subCfg, EventsCfg: eventsCfg, RecommendationCfg: recCfg, DataDir: dataDir, BrandingCfg: brandingCfg, CoverEnricher: coverEnricher, CoverSettings: coverSettings, LibraryScanner: libraryScanner, ScanCfg: scanCfg, Scheduler: scheduler}
 }
 
 func (s *Server) Router() http.Handler {
@@ -139,7 +138,7 @@ func (s *Server) Router() http.Handler {
 		if bus == nil {
 			bus = eventbus.New()
 		}
-		api.Mount(r, s.Pool, s.Logger, writer, s.RecommendationCfg, lidarrCfg, lidarrReqs, lidarrQuar, tracksSvc, playlistsSvc, s.CoverEnricher, s.CoverArtBackfillCap, s.CoverSettings, s.LibraryScanner, s.ScanCfg, s.Scheduler, s.DataDir, smtpSender, bus, s.PlaylistScheduler)
+		api.Mount(r, s.Pool, s.Logger, writer, s.RecommendationCfg, lidarrCfg, lidarrReqs, lidarrQuar, tracksSvc, playlistsSvc, s.CoverEnricher, s.CoverSettings, s.LibraryScanner, s.ScanCfg, s.Scheduler, s.DataDir, smtpSender, bus, s.PlaylistScheduler)
 		// /api/admin/scan is the only admin route owned by the server package
 		// (it needs the Scanner). Register it as a single inline-middleware
 		// route — using r.Route("/api/admin", ...) here would create a second

internal/server/server_test.go

@@ -24,7 +24,7 @@ import (
 )
 
 func TestHealthz(t *testing.T) {
-	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{}, nil)
+	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, nil, nil, library.RunScanConfig{}, nil)
 	ts := httptest.NewServer(s.Router())
 	defer ts.Close()
 
@@ -73,7 +73,7 @@ func TestHealthz_IncludesMinClientVersion(t *testing.T) {
 }
 
 func TestRouter_ServesSPAAtRoot(t *testing.T) {
-	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{}, nil)
+	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, nil, nil, library.RunScanConfig{}, nil)
 	ts := httptest.NewServer(s.Router())
 	defer ts.Close()
 
@@ -92,7 +92,7 @@ func TestRouter_ServesSPAAtRoot(t *testing.T) {
 }
 
 func TestRouter_DeepLinkFallbackReturnsSPA(t *testing.T) {
-	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{}, nil)
+	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, nil, nil, library.RunScanConfig{}, nil)
 	ts := httptest.NewServer(s.Router())
 	defer ts.Close()
 
@@ -111,7 +111,7 @@ func TestRouter_DeepLinkFallbackReturnsSPA(t *testing.T) {
 }
 
 func TestRouter_APIPathNotSwallowedBySPA(t *testing.T) {
-	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{}, nil)
+	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, nil, nil, library.RunScanConfig{}, nil)
 	ts := httptest.NewServer(s.Router())
 	defer ts.Close()
 
@@ -130,7 +130,7 @@ func TestRouter_APIPathNotSwallowedBySPA(t *testing.T) {
 }
 
 func TestRouter_RestPathNotSwallowedBySPA(t *testing.T) {
-	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{}, nil)
+	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, nil, nil, library.RunScanConfig{}, nil)
 	ts := httptest.NewServer(s.Router())
 	defer ts.Close()
 
@@ -206,7 +206,7 @@ func TestRouter_AdminSubtreeNotShadowed(t *testing.T) {
 	}
 
 	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), pool,
-		stubScanner{}, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{}, nil)
+		stubScanner{}, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, nil, nil, library.RunScanConfig{}, nil)
 	ts := httptest.NewServer(s.Router())
 	defer ts.Close()
 

internal/similarity/worker.go

@@ -1,9 +1,9 @@
 // Package similarity owns the inbound ListenBrainz similarity ingest
-// pipeline. A periodic worker queries LB's /explore/similar-recordings
+// pipeline. A periodic worker queries the LB Labs API
-// and /explore/similar-artists endpoints for tracks the user has played,
+// (labs.api.listenbrainz.org similar-recordings / similar-artists) for
-// filters returned MBIDs to the local library, and stores the top-K
+// tracks the user has played, filters returned MBIDs to the local
-// edges in track_similarity / artist_similarity for M4c's radio
+// library, and stores the top-K edges in track_similarity /
-// candidate-pool builder.
+// artist_similarity for M4c's radio candidate-pool builder.
 package similarity
 
 import (
@@ -34,14 +34,16 @@ type Worker struct {
 }
 
 // NewWorker constructs a worker with production defaults: 1h tick,
-// batch=5, topK=20.
+// batch=25, topK=20. batch is tracks AND artists processed per tick;
+// at 25/h a freshly-played library converges in hours, not days, while
+// staying well under ListenBrainz rate limits (429s abort the tick).
 func NewWorker(pool *pgxpool.Pool, client *listenbrainz.Client, logger *slog.Logger) *Worker {
 	return &Worker{
 		pool:   pool,
 		client: client,
 		logger: logger,
 		tick:   1 * time.Hour,
-		batch:  5,
+		batch:  25,
 		topK:   20,
 	}
 }

internal/similarity/worker_test.go

@@ -13,8 +13,8 @@ func TestNewWorker_DefaultsMatchSpec(t *testing.T) {
 	if w.tick != 1*time.Hour {
 		t.Errorf("tick = %v, want 1h", w.tick)
 	}
-	if w.batch != 5 {
+	if w.batch != 25 {
-		t.Errorf("batch = %d, want 5", w.batch)
+		t.Errorf("batch = %d, want 25", w.batch)
 	}
 	if w.topK != 20 {
 		t.Errorf("topK = %d, want 20", w.topK)

web/src/lib/api/admin.covers.test.ts

@@ -25,9 +25,9 @@ describe('admin covers API', () => {
   });
 
   it('refetchMissingCovers POSTs to the bulk endpoint', async () => {
-    (api.post as unknown as ReturnType<typeof vi.fn>).mockResolvedValueOnce({ queued: 7 });
+    (api.post as unknown as ReturnType<typeof vi.fn>).mockResolvedValueOnce({ started: true });
     const got = await refetchMissingCovers();
     expect(api.post).toHaveBeenCalledWith('/api/admin/covers/refetch-missing', {});
-    expect(got.queued).toBe(7);
+    expect(got.started).toBe(true);
   });
 });

web/src/lib/api/admin.ts

@@ -187,7 +187,7 @@ export async function refetchAlbumCover(albumId: string): Promise<RefetchAlbumCo
 }
 
 export type RefetchMissingResponse = {
-  queued: number;
+  started: boolean;
 };
 
 export async function refetchMissingCovers(): Promise<RefetchMissingResponse> {

web/src/routes/admin/+page.svelte

@@ -318,8 +318,10 @@
     bulkBusy = true;
     bulkResult = null;
     try {
-      const { queued } = await refetchMissingCovers();
+      const { started } = await refetchMissingCovers();
-      bulkResult = `Queued ${queued} albums for cover refetch.`;
+      bulkResult = started
+        ? 'Refetching all missing covers — local sources are fast, remote providers throttle per their limits.'
+        : 'Could not start the cover refetch.';
       await client.invalidateQueries({ queryKey: qk.coverage() });
     } catch (e) {
       bulkResult = `Failed: ${errCode(e)}`;

web/src/routes/admin/admin.test.ts

@@ -41,7 +41,7 @@ vi.mock('$lib/api/admin', async () => {
     deleteQuarantineFile: vi.fn().mockResolvedValue({}),
     deleteQuarantineViaLidarr: vi.fn().mockResolvedValue({}),
     triggerScan: vi.fn().mockResolvedValue({}),
-    refetchMissingCovers: vi.fn().mockResolvedValue({ queued: 0 }),
+    refetchMissingCovers: vi.fn().mockResolvedValue({ started: true }),
     researchMissingArt: vi.fn().mockResolvedValue({ version: 1 }),
     createScanScheduleQuery: vi.fn(() =>
       readable({