feat: MusicBrainz proxy API routes (artist search + discography browse)

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

web/src/app/api/mb/artists/[mbid]/releases/route.test.ts

@@ -0,0 +1,30 @@
+import { describe, it, expect, vi, afterEach } from "vitest";
+
+vi.mock("@/lib/musicbrainz", () => ({ browseReleaseGroups: vi.fn() }));
+import { browseReleaseGroups } from "@/lib/musicbrainz";
+import { GET } from "./route";
+
+const mockBrowse = vi.mocked(browseReleaseGroups);
+// NOTE: reset in afterEach, not beforeEach - see the matching note in
+// ../route.test.ts and task-2-report.md for the root cause.
+afterEach(() => mockBrowse.mockReset());
+
+const ctx = (mbid: string) => ({ params: Promise.resolve({ mbid }) });
+
+describe("GET /api/mb/artists/[mbid]/releases", () => {
+  it("returns the discography", async () => {
+    mockBrowse.mockResolvedValue([
+      { rgMbid: "rg1", title: "Continuum", primaryType: "Album", secondaryTypes: [], firstReleaseDate: "2006" },
+    ]);
+    const res = await GET(new Request("http://localhost/x"), ctx("a1"));
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    expect(body.releases[0].rgMbid).toBe("rg1");
+    expect(mockBrowse).toHaveBeenCalledWith("a1");
+  });
+
+  it("502s when MusicBrainz throws", async () => {
+    mockBrowse.mockRejectedValue(new Error("boom"));
+    expect((await GET(new Request("http://localhost/x"), ctx("a1"))).status).toBe(502);
+  });
+});

web/src/app/api/mb/artists/[mbid]/releases/route.ts

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

web/src/app/api/mb/artists/route.test.ts

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+import { describe, it, expect, vi, afterEach } from "vitest";
+
+vi.mock("@/lib/musicbrainz", () => ({ searchArtists: vi.fn() }));
+import { searchArtists } from "@/lib/musicbrainz";
+import { GET } from "./route";
+
+const mockSearch = vi.mocked(searchArtists);
+// NOTE: reset in afterEach, not beforeEach (deviation from the brief - see task-2-report.md).
+// In this Vitest 2.1.8 + Node 22.23.1 environment, resetting a vi.mock()-produced spy in
+// beforeEach causes a later mockRejectedValue() + await/catch in the same test to be
+// misreported as a failing test, even though the rejection is handled correctly. Moving the
+// identical reset call to afterEach gives the same inter-test isolation and avoids the false
+// failure. Reproduced independent of this repo (bare vitest 2.1.8/2.1.9/3.2.4 project) and
+// independent of the Node wrapper (same result with the raw fnm-installed node binary).
+afterEach(() => mockSearch.mockReset());
+
+function req(q: string | null) {
+  return new Request(`http://localhost/api/mb/artists${q === null ? "" : `?q=${encodeURIComponent(q)}`}`);
+}
+
+describe("GET /api/mb/artists", () => {
+  it("returns hits for a query", async () => {
+    mockSearch.mockResolvedValue([{ mbid: "a1", name: "John Mayer", disambiguation: "" }]);
+    const res = await GET(req("john"));
+    expect(res.status).toBe(200);
+    expect((await res.json()).artists[0].name).toBe("John Mayer");
+  });
+
+  it("400s a blank query", async () => {
+    expect((await GET(req("  "))).status).toBe(400);
+    expect((await GET(req(null))).status).toBe(400);
+  });
+
+  it("502s when MusicBrainz throws", async () => {
+    mockSearch.mockRejectedValue(new Error("MusicBrainz request failed: 503"));
+    expect((await GET(req("john"))).status).toBe(502);
+  });
+});

web/src/app/api/mb/artists/route.ts

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+import { searchArtists } from "@/lib/musicbrainz";
+
+export async function GET(request: Request) {
+  const q = new URL(request.url).searchParams.get("q");
+  if (!q || !q.trim()) {
+    return Response.json({ error: "q is required" }, { status: 400 });
+  }
+  try {
+    return Response.json({ artists: await searchArtists(q.trim()) });
+  } catch {
+    return Response.json({ error: "MusicBrainz unavailable" }, { status: 502 });
+  }
+}