Two approved composition changes (#1269), mechanism only — the
taste/fresh share stays data-decided (#1252) and pick_kind
attribution is unchanged.
Multi-seed blending: each day's build now seeds from up to 3 of the
user's top-5 tracks (pickDailySeeds, the generalized daily shuffle)
instead of one rotating anchor, so the mix spans neighborhoods within
a day and stops feeling bipolar as the rotation swings between
dissimilar seeds. Per-seed pools merge first-seen-deduped; the head
is filled best-first under 50/30/20 per-seed quotas (60/40 for two
seeds) so one neighborhood can't monopolize it, with thin-seed quota
spilling best-first.
Score-weighted fresh tail: the tail sample (rank 2*headN onward) was
uniform — the 380th-best candidate as likely as the 101st. It now
uses deterministic Efraimidis-Spirakis keys with weight halving every
50 ranks, so freshness keeps its "you'll probably enjoy this" half
while still rotating daily.
The retired single-seed picker's one other caller, You-might-like,
moves to pickDailySeeds(n=1) — a single neighborhood per day is right
for a short shelf, and the behavior note is inline.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TsF3cNoKrqCYsU78cXC8U6
Milestone #127 step 2 (#1249). For You deliberately blends two
populations — a head of top-scored taste picks and a tail sampled from
deeper ranking (the freshness injection) — but the metrics judged it as
one blob, so its skip rate couldn't distinguish "the taste engine is
missing" from "the freshness tax is too high". That number decides the
exploration share before we tune it.
- Migration 0038: nullable pick_kind ('taste'|'fresh') on both
playlist_tracks (stamped at snapshot build) and play_events (frozen at
play-ingestion — the snapshot rebuilds daily, so attribution cannot be
reconstructed at read time).
- Builder: pickHeadAndTail marks head=taste / tail=fresh; the small-pool
fallback is all taste (top-N-by-score IS the taste mechanism). Other
variants persist NULL.
- Ingestion: for_you plays (live + offline replay) look the track up in
the user's current snapshot; not found → unattributed, never guessed.
- Metrics: For You's row gains a breakdown (taste / fresh / earlier
unattributed plays), parent row stays the sum; web card renders the
sub-rows indented with the same baseline deltas + low-data dimming.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TsF3cNoKrqCYsU78cXC8U6
Five diversity mechanics — applied to both For-You and Songs-Like-X.
1. For-You seed rotates daily across the user's top-5 most-played
tracks. pickForYouSeedForDay uses userIDHash(user, day) mod
len(seeds) so today's mix uses an entirely different similarity
pool than tomorrow's. Within-day determinism preserved.
2. JitterMagnitude bumped 0.0 → 0.1. The scoring RNG is now seeded
by userIDHash(user, day) rather than the no-op, so near-tied
candidates shuffle daily without breaking within-day stability.
3. Head/tail split moves from 20+5 to 12+13. Roughly half the
playlist comes from the tail now (daily-deterministic via
tieBreakHash), giving the user substantially different content
while a 12-track anchor of strong similarity matches keeps the
mix recognizable.
4. Songs-Like-X seed artists shuffle daily across the user's top-5
played artists. pickSeedArtistsForDay applies a userIDHash-seeded
Fisher-Yates and takes 3.
5. scoreAndSortCandidates / pickTopN / pickHeadAndTail gain a userID
parameter so the RNG can be seeded per-user; existing call sites
updated; noopRNG removed.
Test fixtures widened similarity gaps (e.g. float64(50-i) instead of
(50-i)/50) so the new jitter (±0.1) doesn't perturb head ordering in
assertions about the head/tail mechanism. New seed_selection_test
coverage for userIDHash + pickForYouSeedForDay + pickSeedArtistsForDay
spans deterministic-within-day, varies-across-days, and graceful
degradation with small candidate pools.
PickTopPlayedTrackForUser replaced by PickTopPlayedTracksForUser
:many in the prior commit (b4801c2). The For-You seed lookup now
goes through pickForYouSeedForDay over the returned slice.
PickSeedArtists's LIMIT widened to 5 in the same prior commit.
For #392 Half A — system playlist content diversity. Half B
(per-user timezone scheduling) is a separate spec.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Two improvements to the system playlist builder:
1. Per-artist (<=3) and per-album (<=2) caps applied to the
pickTopN truncation step, using the same numeric caps Discover
already enforces. Both For-You and Songs-like-X benefit. Same
skewed candidate pool no longer collapses to "10 tracks from
the same artist" — the playlist always carries at least 9
distinct artists in 25 slots.
2. New pickHeadAndTail function for For-You: 20 top-similarity
tracks + 5 sampled from the tail (positions 2*headN onward of
the score-sorted, cap-applied pool). Tail sampling uses
tieBreakHash for daily determinism — same user same day still
sees the same playlist, but the daily refresh feels less
stuck-in-a-rut. Tail tracks are still similarity-related
(they passed the similarity candidate filter) so the user
should enjoy them, just from artists they wouldn't have surfaced
via strict top-N ranking.
Songs-like-X keeps the simple pickTopN call — the seed-artist
context already provides the "you'll like this" framing without
needing a tail injection.
Refactors pickTopN internals: now sorts candidates first via
scoreAndSortCandidates, applies the cap on []Candidate via
capCandidatesByAlbumAndArtist, and truncates. Removes the now-
dead stableSortByScoreThenHash helper (only used in old pickTopN).
The cap helper mirrors capByAlbumAndArtist in discover.go but
operates on recommendation.Candidate so it sees Track.AlbumID /
Track.ArtistID directly.
Tests cover the cap helper truth table, head+tail split with
small/large pools, buffer-zone exclusion, daily determinism, and
cross-day tail variance.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
bvandeusen