feat(discover): time-boxed suggestion snooze, server side — #2374

Migration 0049 adds suggestion_snoozes(user_id, candidate_mbid,
candidate_name, snoozed_until), and SuggestArtistsForUser excludes rows
whose snooze hasn't expired.

This is NOT a dislike. Rule #101 forbids a "Not for me" / thumbs-down
UI; a snooze is the approved shape instead because it records no verdict
on the music, expires on its own (~90d), and never reaches the taste
profile. It's acquisition triage — "not right now" — so the filter sits
at the candidate stage rather than in the score, where it would become a
ranking signal by the back door.

Per-user throughout (rule #47): one household member parking a candidate
leaves everyone else's deck untouched.

candidate_name is denormalized because suggestions are out-of-library by
definition — there is no artists row to resolve a display name from, and
the un-snooze list has to show something. That list is why GET
/discover/snoozes exists at all: a parked candidate is by definition
absent from the deck, so without it the DELETE would be unreachable.

Also fixes a hole in the codegen check from #2380: `git diff` ignores
untracked paths, so a brand-new generated file would have passed it
silently. `git add -N` first. This commit is the first to add one.

Endpoints:
  POST   /api/discover/suggestions/{mbid}/snooze  (body: name, days)
  DELETE /api/discover/suggestions/{mbid}/snooze
  GET    /api/discover/snoozes

UI lands in slice 4 (#2375) before any of this merges — rule #27.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

internal/db/queries/recommendation.sql

@@ -272,8 +272,9 @@ LIMIT 1;
 -- undamped sum let one heavily-played artist's neighbours take every slot --
 -- entrenching harder the MORE the user listened (issue #2367 mechanism 2).
 --
--- Candidates already in the library, or already requested and not terminal,
--- are excluded. $1=user_id, $2=half_life_days (tier 2 decay), $3=limit.
+-- Candidates already in the library, already requested and not terminal, or
+-- snoozed by this user, are excluded. $1=user_id, $2=half_life_days (tier 2
+-- decay), $3=limit.
 WITH artist_plays AS (
     -- Completed plays only. The previous seed query counted every play_event,
     -- so skipping an artist repeatedly INCREASED its signal and pushed more of
@@ -334,6 +335,18 @@ contributions AS (
              AND r.lidarr_artist_mbid = u.candidate_mbid
              AND r.status NOT IN ('rejected', 'failed')
       )
+      -- Snoozed by this user and not yet expired (#2374). Time-boxed and
+      -- per-user: the candidate returns on its own once snoozed_until
+      -- passes, and stays visible to everyone else meanwhile. Deliberately
+      -- filtered at the candidate stage, NOT folded into the score — a
+      -- snooze carries no opinion about the music, so it must not become a
+      -- ranking signal.
+      AND NOT EXISTS (
+          SELECT 1 FROM suggestion_snoozes s
+           WHERE s.user_id = $1
+             AND s.candidate_mbid = u.candidate_mbid
+             AND s.snoozed_until > now()
+      )
 )
 SELECT candidate_mbid,
        candidate_name,

internal/db/queries/suggestion_snoozes.sql

@@ -0,0 +1,39 @@
+-- Time-boxed "not right now" on a Discover artist suggestion (#2374).
+--
+-- See 0049_suggestion_snoozes.up.sql for why this is a snooze and not a
+-- dismissal: it records no verdict on the music, expires on its own, and
+-- must never reach the taste profile. Nothing in internal/taste may read
+-- this table.
+
+-- name: SnoozeSuggestion :exec
+-- Upsert, so re-snoozing an already-snoozed candidate EXTENDS it instead of
+-- erroring on the PK. The name is refreshed too — a later suggestion may
+-- carry a corrected spelling from the similarity feed.
+-- $1=user_id, $2=candidate_mbid, $3=candidate_name, $4=duration in days.
+INSERT INTO suggestion_snoozes (user_id, candidate_mbid, candidate_name, snoozed_until)
+VALUES ($1, $2, $3, now() + ($4::float8 * INTERVAL '1 day'))
+ON CONFLICT (user_id, candidate_mbid) DO UPDATE
+   SET snoozed_until  = EXCLUDED.snoozed_until,
+       candidate_name = EXCLUDED.candidate_name;
+
+-- name: UnsnoozeSuggestion :execrows
+-- Row count is returned so the handler can 404 an MBID that was never
+-- snoozed rather than reporting success for a no-op.
+DELETE FROM suggestion_snoozes
+ WHERE user_id = $1 AND candidate_mbid = $2;
+
+-- name: ListActiveSuggestionSnoozes :many
+-- Backs the manage / un-snooze surface. Expired rows are filtered HERE
+-- rather than left to the sweeper: gc runs on an hourly tick, so a row can
+-- outlive its expiry by up to a tick and must not read as still-snoozed in
+-- the meantime.
+SELECT candidate_mbid, candidate_name, snoozed_until, created_at
+  FROM suggestion_snoozes
+ WHERE user_id = $1 AND snoozed_until > now()
+ ORDER BY snoozed_until, candidate_mbid;
+
+-- name: GcDeleteExpiredSuggestionSnoozes :execrows
+-- Keeps the table from growing without bound. Every read already filters on
+-- snoozed_until > now(), so deleting an expired row changes no behaviour —
+-- this is purely reclamation.
+DELETE FROM suggestion_snoozes WHERE snoozed_until < now();