feat(preview): GET /api/mb/release-groups/[rgMbid]/tracks

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/app/api/mb/release-groups/[rgMbid]/tracks/route.test.ts

@@ -0,0 +1,27 @@
+import { describe, it, expect, vi, afterEach } from "vitest";
+
+vi.mock("@/lib/musicbrainz", () => ({ browseReleaseGroupTracks: vi.fn() }));
+import { browseReleaseGroupTracks } from "@/lib/musicbrainz";
+import { GET } from "./route";
+
+const mock = vi.mocked(browseReleaseGroupTracks);
+afterEach(() => mock.mockReset());
+
+function get(rgMbid: string) {
+  return GET(new Request(`http://localhost/api/mb/release-groups/${rgMbid}/tracks`), {
+    params: Promise.resolve({ rgMbid }),
+  });
+}
+
+describe("release-group tracks API", () => {
+  it("returns tracks", async () => {
+    mock.mockResolvedValue([{ position: 1, title: "One", lengthMs: 1000 }]);
+    const body = await (await get("rg1")).json();
+    expect(body.tracks).toEqual([{ position: 1, title: "One", lengthMs: 1000 }]);
+  });
+
+  it("502s on MB failure", async () => {
+    mock.mockRejectedValue(new Error("down"));
+    expect((await get("rg1")).status).toBe(502);
+  });
+});

web/src/app/api/mb/release-groups/[rgMbid]/tracks/route.ts

@@ -0,0 +1,10 @@
+import { browseReleaseGroupTracks } from "@/lib/musicbrainz";
+
+export async function GET(_request: Request, { params }: { params: Promise<{ rgMbid: string }> }) {
+  const { rgMbid } = await params;
+  try {
+    return Response.json({ tracks: await browseReleaseGroupTracks(rgMbid) });
+  } catch {
+    return Response.json({ error: "MusicBrainz unavailable" }, { status: 502 });
+  }
+}