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/routes/dumps.ts

@@ -8,6 +8,7 @@ import {
   isCreateUrlDumpRequest,
   isUpdateDumpRequest,
   type PaginatedData,
+  type Playlist,
 } from "../model/interfaces.ts";
 
 import { authMiddleware } from "../middleware/auth.ts";
@@ -30,6 +31,7 @@ import {
 } from "../services/dump-service.ts";
 import { getDumpVoters } from "../services/vote-service.ts";
 import { getRelatedDumps } from "../services/backlink-service.ts";
+import { getPlaylistsForDump } from "../services/playlist-service.ts";
 
 const router = new Router({ prefix: "/api/dumps" });
 
@@ -128,6 +130,18 @@ router.get("/:dumpId/related", async (ctx) => {
   ctx.response.body = responseBody;
 });
 
+router.get("/:dumpId/playlists", async (ctx) => {
+  const requestingUserId = await parseOptionalAuth(ctx) ?? undefined;
+  // Resolve through getDump so private dumps 404 for anyone but their owner.
+  const dump = getDump(ctx.params.dumpId, requestingUserId);
+  const playlists = getPlaylistsForDump(dump.id, requestingUserId);
+  const responseBody: APIResponse<Playlist[]> = {
+    success: true,
+    data: playlists,
+  };
+  ctx.response.body = responseBody;
+});
+
 router.get("/", async (ctx) => {
   const requestingUserId = await parseOptionalAuth(ctx) ?? undefined;
   const { page, limit } = parsePagination(ctx.request.url.searchParams);

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 {