fix(playlists): allow the 5 discovery-mix variants in DB constraints

HOTFIX for v2026.05.15.0. R3 added deep_cuts/rediscover/new_for_you/
on_this_day/first_listens producers + registry entries but not their
system_variant values to the playlists_kind_variant_consistent /
playlists_seed_consistent CHECK constraints (0021's whitelist).
insertSystemPlaylist for any new mix → SQLSTATE 23514, and since
BuildSystemPlaylists is one all-or-nothing txn that aborts the
ENTIRE build — For-You/Discover refresh 500s and the daily lazy
build fails too. System playlists are fully broken in prod.

Migration 0028 drops + re-adds both constraints with all five new
seedless variants (mirrors the 0021 drop-and-readd pattern).
CHECK-only — sqlc/dbq unaffected (regen produced no drift).

Bumps to 2026.5.15+7 for the v2026.05.15.1 patch release.

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

internal/db/migrations/0028_discovery_mix_variants.down.sql

@@ -0,0 +1,24 @@
+-- Reverts to the 0021 constraint set (for_you, songs_like_artist,
+-- discover only). Fails if any playlists row still has one of the
+-- five new system_variant values — delete/rebuild system playlists
+-- first if rolling back.
+
+ALTER TABLE playlists DROP CONSTRAINT IF EXISTS playlists_kind_variant_consistent;
+ALTER TABLE playlists
+    ADD CONSTRAINT playlists_kind_variant_consistent CHECK (
+        (kind = 'user'   AND system_variant IS NULL)
+        OR
+        (kind = 'system' AND system_variant IN ('for_you', 'songs_like_artist', 'discover'))
+    );
+
+ALTER TABLE playlists DROP CONSTRAINT IF EXISTS playlists_seed_consistent;
+ALTER TABLE playlists
+    ADD CONSTRAINT playlists_seed_consistent CHECK (
+        (system_variant IS NULL                 AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'for_you'             AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'discover'            AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'songs_like_artist'   AND seed_artist_id IS NOT NULL)
+    );

internal/db/migrations/0028_discovery_mix_variants.up.sql

@@ -0,0 +1,47 @@
+-- #411 R3 bugfix: the five discovery mixes (deep_cuts, rediscover,
+-- new_for_you, on_this_day, first_listens) were added as producers +
+-- registry entries but their system_variant values were never added
+-- to the two playlists CHECK constraints. Result: insertSystemPlaylist
+-- for any new mix fails with playlists_kind_variant_consistent
+-- (SQLSTATE 23514), which — because BuildSystemPlaylists is one
+-- all-or-nothing transaction — aborts the WHOLE build, so For-You /
+-- Discover refresh 500s and the lazy daily build fails too.
+--
+-- All five are seedless (like for_you/discover): seed_artist_id IS
+-- NULL. Drop + re-add both constraints with the expanded set, same
+-- pattern as 0021_discover_variant (Postgres has no ALTER CONSTRAINT
+-- for CHECK).
+
+ALTER TABLE playlists DROP CONSTRAINT IF EXISTS playlists_kind_variant_consistent;
+ALTER TABLE playlists
+    ADD CONSTRAINT playlists_kind_variant_consistent CHECK (
+        (kind = 'user'   AND system_variant IS NULL)
+        OR
+        (kind = 'system' AND system_variant IN (
+            'for_you', 'songs_like_artist', 'discover',
+            'deep_cuts', 'rediscover', 'new_for_you',
+            'on_this_day', 'first_listens'
+        ))
+    );
+
+ALTER TABLE playlists DROP CONSTRAINT IF EXISTS playlists_seed_consistent;
+ALTER TABLE playlists
+    ADD CONSTRAINT playlists_seed_consistent CHECK (
+        (system_variant IS NULL                 AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'for_you'             AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'discover'            AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'deep_cuts'           AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'rediscover'          AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'new_for_you'         AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'on_this_day'         AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'first_listens'       AND seed_artist_id IS NULL)
+        OR
+        (system_variant = 'songs_like_artist'   AND seed_artist_id IS NOT NULL)
+    );