bvandeusenandClaude Opus 5
b27029f674
Second half of the reported symptom: suggestions "show the same artists until you request one". The ranking was `ORDER BY total_score DESC` with no randomization and no seen-state, so the only things that could ever change the deck were a candidate entering the library or the user filing a request. The tail of the ranking was unreachable — requesting was literally the only lever. No SQL change was needed. The query already takes a limit, so it over-fetches a pool (4x the slots, capped at 60) and the selection moves to Go, where it is a pure function of (pool, limit, day) — no DB, no clock — and therefore unit testable in the fast lane instead of behind the integration gate. Three rules. The best few by score always lead, so the strongest matches never rotate out of sight (For You's head/tail shape). The remaining slots are drawn by md5(mbid + day), the same daily-stable idiom the Home rows already use: stable within a day so pull-to-refresh doesn't reshuffle, different tomorrow, and no stored state. And a per-seed cap keeps roughly a quarter of the deck attributable to any one seed artist, so twelve neighbours of a single artist can't be the whole surface. The cap is a preference, not a quota. A user whose pool hangs off one or two seeds would otherwise get a three-card surface — worse than the monoculture being avoided, and exactly the vanish-or-nothing shape rule #131 exists to prevent — so a short deck tops up in score order from what the cap set aside. This is also what keeps the existing Top12Cap integration test honest: its 30 candidates share one seed, and without the top-up it would return 3. Eight unit tests, including one that had to be rewritten mid-change: the first version asserted the cap against an evenly-spread pool, where the top-N is already diverse and the assertion could not fail. It now uses a skewed pool where one seed owns the entire top of the ranking, which is the only shape that actually exercises a cap. Dropped two //nolint:gosec directives added in passing — gosec isn't in .golangci.yml, so they suppressed nothing and only implied a check that runs. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>