fix(models): support single model lookup

Support single model lookup by replacing the one-segment models route
with a catch-all route that preserves capability kind paths while
allowing provider-prefixed IDs like cc/claude-sonnet-5.

tests/unit/v1-model-lookup-3588.test.js

@@ -0,0 +1,71 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const mocks = vi.hoisted(() => ({
+  buildModelsList: vi.fn(),
+}));
+
+vi.mock("../../src/app/api/v1/models/route.js", () => ({
+  buildModelsList: mocks.buildModelsList,
+}));
+
+const { GET } = await import("../../src/app/api/v1/models/[...model]/route.js");
+
+const chatModel = {
+  id: "cc/claude-sonnet-5",
+  object: "model",
+  owned_by: "cc",
+  context_length: 1_000_000,
+};
+
+function params(model) {
+  return { params: Promise.resolve({ model }) };
+}
+
+describe("GET /v1/models/{id}", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("retrieves a provider-prefixed model ID split across URL path segments", async () => {
+    mocks.buildModelsList.mockResolvedValue([chatModel]);
+
+    const response = await GET(new Request("https://router.test/v1/models/cc/claude-sonnet-5"), params(["cc", "claude-sonnet-5"]));
+
+    expect(response.status).toBe(200);
+    expect(await response.json()).toEqual(chatModel);
+    expect(mocks.buildModelsList).toHaveBeenCalledWith(["llm"]);
+  });
+
+  it("also handles a decoded slash in a single catch-all segment", async () => {
+    mocks.buildModelsList.mockResolvedValue([chatModel]);
+
+    const response = await GET(new Request("https://router.test/v1/models/cc%2Fclaude-sonnet-5"), params(["cc/claude-sonnet-5"]));
+
+    expect(response.status).toBe(200);
+    expect(await response.json()).toEqual(chatModel);
+  });
+
+  it("keeps capability-list routes unchanged", async () => {
+    const imageModel = { id: "image/gpt-image-1", object: "model", owned_by: "image" };
+    mocks.buildModelsList.mockResolvedValue([imageModel]);
+
+    const response = await GET(new Request("https://router.test/v1/models/image"), params(["image"]));
+
+    expect(response.status).toBe(200);
+    expect(await response.json()).toEqual({ object: "list", data: [imageModel] });
+    expect(mocks.buildModelsList).toHaveBeenCalledWith(["image"]);
+  });
+
+  it("returns an OpenAI-style model_not_found response for an unknown model", async () => {
+    mocks.buildModelsList.mockResolvedValue([chatModel]);
+
+    const response = await GET(new Request("https://router.test/v1/models/cc/missing-model"), params(["cc", "missing-model"]));
+    const body = await response.json();
+
+    expect(response.status).toBe(404);
+    expect(body.error).toMatchObject({
+      type: "invalid_request_error",
+      code: "model_not_found",
+    });
+  });
+});