User request 2026-06-01: the previous Rediscover only fired on
explicit album/artist likes, so users who only liked at the track
level got an empty Rediscover row. Also no daily rotation - the
section never changed between data updates - and 25 items felt long
for the Home carousel.
SQL (internal/db/queries/recommendation.sql):
- ListRediscoverAlbumsForUser UNIONs the existing explicit album-like
signal with a new track-derived path: an album qualifies if it has
>=2 liked tracks where the earliest like is >30 days old.
- ListRediscoverArtistsForUser does the same with threshold 3 (artists
span more releases, so the bar is higher to avoid one-hit-wonder
affinities).
- Both ordering switched from longest-since-last-play to a daily-
stable random hash md5(entity_id || user_id || current_date) so
the row randomizes but stays consistent within a day.
- Fallback queries also switched to the daily-stable hash so the
fallback rows don't reshuffle on every refresh.
Go (internal/recommendation/home.go):
- HomeRediscoverLimit dropped from 25 to 10 (carousel-sized).
- rediscoverInnerLimit (30) is the per-query cap; gives headroom so
the Go-layer filters don't undershoot.
- applyRediscoverAlbumFilters does cross-section dedup vs Most Played
(no point surfacing albums the user is actively spinning) plus a
diversity cap of max 2 albums per artist (prevents one liked-but-
forgotten artist dominating the row).
- applyRediscoverArtistFilters does cross-section dedup vs Most
Played's artist set; no diversity cap needed (one row per artist).
Tests (internal/recommendation/home_integration_test.go):
- TrackDerived path: 2 liked tracks >30d old + no recent plays = album
appears in Rediscover.
- Threshold guard: 1 liked track = album does NOT appear.
- Diversity cap: 4 explicit album-likes from same artist = 2 in output.
- Dedup vs MostPlayed: eligible album whose track is in MostPlayed
gets filtered out.
- Existing FallbackWhenSparse test preserved (semantics unchanged for
recent likes that miss the >30d primary filter).
Clients unchanged - they render whatever /api/home/index returns. No
parity-map row needed (this is a server-internal recommendation
change, not a layout divergence).
Replaces var _ = func() pgtype.UUID { ... } with var _ map[pgtype.UUID]struct{}
which actually verifies map-key comparability, matching the comment.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Runs five SQL queries in parallel (recently added albums, most played
tracks, last played artists, rediscover albums, rediscover artists) via
goroutines with mutex-guarded first-error capture. Rediscover sections
merge primary + fallback results, de-duping by pgtype.UUID map key.
All HomePayload slices are non-nil so the API handler encodes [] not null.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
bvandeusen