v3: added an "in collections" section to dump pages, listing the collections a dump belongs to

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

api/services/playlist-service.ts

@@ -382,6 +382,26 @@ export function getPlaylistMembershipsForDump(
   });
 }
 
+/**
+ * The playlists a dump appears in — the "in collections" counterpart to
+ * backlinks. Privacy-filtered like `getRelatedDumps`: public playlists for
+ * everyone, plus the requesting user's own private ones. Capped at 20 — a
+ * small, bounded list of supporting context.
+ */
+export function getPlaylistsForDump(
+  dumpId: string,
+  requestingUserId?: string,
+): Playlist[] {
+  const rows = db.prepare(
+    `SELECT ${PLAYLIST_SELECT}
+     INNER JOIN playlist_dumps pd ON pd.playlist_id = p.id
+     WHERE pd.dump_id = ? AND (p.is_public = 1 OR p.user_id = ?)
+     ORDER BY p.created_at DESC LIMIT 20;`,
+  ).all(dumpId, requestingUserId ?? "");
+
+  return rows.filter(isPlaylistRow).map(playlistRowToApi);
+}
+
 export function getPlaylistImageInfo(
   idOrSlug: string,
 ): { id: string; imageMime: string } | undefined {