fix(playlists): robust For-You seed + deep fill; young-library mix fallbacks

For-You silently vanished after ~7 days of not listening (seed query
required a non-skip play in the last 7 days) and capped at ~40 on
self-hosted libraries with no ListenBrainz similarity data.

- PickTopPlayedTracksForUser: tiered seed — last 30d top plays, else
  all-time top plays, else liked tracks. For-You only disappears now
  if the account has zero plays AND zero likes.
- produceForYou uses deeper candidate source limits (raised random/
  tag/similar K) so it reaches ~100 even with empty lb_similar /
  similar_artists; richer when LB enrichment is present.
- Rediscover: tiered — 6-month-dormant, else ≥5-play 30-day-dormant.
- On This Day: floor 60→30 days, window ±7→±10 doy; still skips
  cleanly (no rows → no playlist) on insufficient history.

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

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 ABS(EXTRACT(DOY FROM started_at) - EXTRACT(DOY FROM now())) <= 7
+       AND started_at < now() - interval '30 days'
+       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
-      FROM play_events
-     WHERE user_id = $1 AND was_skipped = false
-     GROUP BY track_id
+    SELECT pe.track_id, COUNT(*) AS c, MAX(pe.started_at) AS last_at
+      FROM play_events pe
+     WHERE pe.user_id = $1 AND pe.was_skipped = false
+     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
-  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
-   )
- ORDER BY s.c DESC, t.id
+SELECT id, album_id, artist_id
+  FROM (
+    SELECT id, album_id, artist_id, c, tier FROM deep
+    UNION ALL
+    SELECT id, album_id, artist_id, c, tier FROM shallow
+     WHERE NOT EXISTS (SELECT 1 FROM deep)
+  ) u
+ ORDER BY tier, c DESC, 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.
-// $1 user_id.
+// has drifted away from. Tiered so a young library still gets a mix:
+//
+//	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
-  FROM play_events pe
-  JOIN tracks t ON t.id = pe.track_id
- WHERE pe.user_id = $1
-   AND pe.started_at > now() - INTERVAL '7 days'
-   AND pe.was_skipped = false
- GROUP BY t.id
- ORDER BY COUNT(*) DESC, t.id
+WITH recent AS (
+    SELECT t.id, COUNT(*) AS c, 0 AS tier
+      FROM play_events pe
+      JOIN tracks t ON t.id = pe.track_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
 `
 
-// For-You candidate seeds. Returns the user's top-5 most-played
-// non-skipped tracks in the last 7 days; tie-break by track_id for
-// determinism. The Go-side picker (pickForYouSeedForDay) chooses one
-// of the returned rows as today's seed via userIDHash so the
-// candidate pool rotates day-to-day while staying stable within a
-// day.
+// For-You candidate seeds, tiered so For-You never silently vanishes:
+//
+//	tier 0  top non-skip plays in the last 30 days
+//	tier 1  (only if tier 0 empty) all-time top non-skip plays
+//	tier 2  (only if tiers 0+1 empty) liked tracks
+//
+// 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/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.
--- $1 user_id.
+-- has drifted away from. Tiered so a young library still gets a mix:
+--   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
-      FROM play_events
-     WHERE user_id = $1 AND was_skipped = false
-     GROUP BY track_id
+    SELECT pe.track_id, COUNT(*) AS c, MAX(pe.started_at) AS last_at
+      FROM play_events pe
+     WHERE pe.user_id = $1 AND pe.was_skipped = false
+     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
-  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
-   )
- ORDER BY s.c DESC, t.id
+SELECT id, album_id, artist_id
+  FROM (
+    SELECT id, album_id, artist_id, c, tier FROM deep
+    UNION ALL
+    SELECT id, album_id, artist_id, c, tier FROM shallow
+     WHERE NOT EXISTS (SELECT 1 FROM deep)
+  ) u
+ ORDER BY tier, c DESC, 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 ABS(EXTRACT(DOY FROM started_at) - EXTRACT(DOY FROM now())) <= 7
+       AND started_at < now() - interval '30 days'
+       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
--- non-skipped tracks in the last 7 days; tie-break by track_id for
--- determinism. The Go-side picker (pickForYouSeedForDay) chooses one
--- of the returned rows as today's seed via userIDHash so the
--- candidate pool rotates day-to-day while staying stable within a
--- day.
-SELECT t.id
-  FROM play_events pe
-  JOIN tracks t ON t.id = pe.track_id
- WHERE pe.user_id = $1
-   AND pe.started_at > now() - INTERVAL '7 days'
-   AND pe.was_skipped = false
- GROUP BY t.id
- ORDER BY COUNT(*) DESC, t.id
+-- For-You candidate seeds, tiered so For-You never silently vanishes:
+--   tier 0  top non-skip plays in the last 30 days
+--   tier 1  (only if tier 0 empty) all-time top non-skip plays
+--   tier 2  (only if tiers 0+1 empty) liked tracks
+-- 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.
+WITH recent AS (
+    SELECT t.id, COUNT(*) AS c, 0 AS tier
+      FROM play_events pe
+      JOIN tracks t ON t.id = pe.track_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/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",