fix(web): wanted POST converges on P2002 unique race instead of 500

Two concurrent Wants for the same release-group both pass the
findUnique existence check as absent; the loser's create() then hits
the rgMbid unique constraint and threw an uncaught P2002, 500ing the
request. Wrap the create in try/catch and fall back to the same
update-and-return-200 path on P2002, converging instead of erroring.
Non-P2002 errors are rethrown unchanged.

web/src/app/api/wanted/route.test.ts

@@ -1,4 +1,5 @@
 import { describe, it, expect, vi, afterEach } from "vitest";
+import { Prisma } from "@prisma/client";
 
 vi.mock("@/lib/musicbrainz", () => ({ searchReleaseGroup: vi.fn() }));
 import { searchReleaseGroup } from "@/lib/musicbrainz";
@@ -51,4 +52,32 @@ describe("wanted API", () => {
     mockSearch.mockRejectedValue(new Error("boom"));
     expect((await POST(postReq({ artist: "X", album: "Y" }))).status).toBe(502);
   });
+
+  it("handles a concurrent duplicate (race between findUnique and create) by converging on 200, never 500", async () => {
+    mockSearch.mockResolvedValue({ rgMbid: "rg-race", title: "Race Condition", primaryType: "Album", secondaryTypes: [], firstReleaseDate: "2010", artistMbid: "a1", artistName: "Racer" });
+    const res = await POST(postReq({ artist: "Racer", album: "Race Condition" }));
+    expect([200, 201]).toContain(res.status);
+    // second identical POST must also be 200 (idempotent), never 500
+    const res2 = await POST(postReq({ artist: "Racer", album: "Race Condition" }));
+    expect(res2.status).toBe(200);
+  });
+
+  it("catches a P2002 thrown by create and falls back to update", async () => {
+    mockSearch.mockResolvedValue({ rgMbid: "rg-p2002", title: "Duplicate", primaryType: "Album", secondaryTypes: [], firstReleaseDate: "2011", artistMbid: "a1", artistName: "Duper" });
+    // Simulate the row already existing when create() is attempted (a concurrent winner beat us to it),
+    // while the pre-create findUnique check still had not seen it — force create() to reject with P2002.
+    await prisma.monitoredRelease.create({ data: { artistMbid: "a1", artistName: "Duper", rgMbid: "rg-p2002", album: "Duplicate", secondaryTypes: [], monitored: false } });
+    const spy = vi.spyOn(prisma.monitoredRelease, "create").mockRejectedValueOnce(
+      new Prisma.PrismaClientKnownRequestError("Unique constraint failed", { code: "P2002", clientVersion: "6.1.0" }),
+    );
+    // Force the pre-create existence check to miss (simulating the race) so we actually reach create().
+    const findUniqueSpy = vi.spyOn(prisma.monitoredRelease, "findUnique").mockResolvedValueOnce(null);
+    const res = await POST(postReq({ artist: "Duper", album: "Duplicate" }));
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    expect(body.monitored).toBe(true);
+    expect(await prisma.monitoredRelease.count({ where: { rgMbid: "rg-p2002" } })).toBe(1);
+    spy.mockRestore();
+    findUniqueSpy.mockRestore();
+  });
 });

web/src/app/api/wanted/route.ts

@@ -1,3 +1,4 @@
+import { Prisma } from "@prisma/client";
 import { prisma } from "@/lib/db";
 import { searchReleaseGroup } from "@/lib/musicbrainz";
 
@@ -49,17 +50,29 @@ export async function POST(request: Request) {
     const updated = await prisma.monitoredRelease.update({ where: { rgMbid: match.rgMbid }, data: { monitored: true } });
     return Response.json({ id: updated.id, album: updated.album, monitored: updated.monitored }, { status: 200 });
   }
-  const created = await prisma.monitoredRelease.create({
+  try {
-    data: {
+    const created = await prisma.monitoredRelease.create({
-      artistMbid: match.artistMbid,
+      data: {
-      artistName: match.artistName,
+        artistMbid: match.artistMbid,
-      rgMbid: match.rgMbid,
+        artistName: match.artistName,
-      album: match.title,
+        rgMbid: match.rgMbid,
-      primaryType: match.primaryType,
+        album: match.title,
-      secondaryTypes: match.secondaryTypes,
+        primaryType: match.primaryType,
-      firstReleaseDate: match.firstReleaseDate,
+        secondaryTypes: match.secondaryTypes,
-      monitored: true,
+        firstReleaseDate: match.firstReleaseDate,
-    },
+        monitored: true,
-  });
+      },
-  return Response.json({ id: created.id, album: created.album, monitored: created.monitored }, { status: 201 });
+    });
+    return Response.json({ id: created.id, album: created.album, monitored: created.monitored }, { status: 201 });
+  } catch (e) {
+    if (e instanceof Prisma.PrismaClientKnownRequestError && e.code === "P2002") {
+      // Concurrent Want for the same release-group won the create; converge to the update path.
+      const updated = await prisma.monitoredRelease.update({
+        where: { rgMbid: match.rgMbid },
+        data: { monitored: true },
+      });
+      return Response.json({ id: updated.id, album: updated.album, monitored: updated.monitored }, { status: 200 });
+    }
+    throw e;
+  }
 }