feat: refine metadata catalog workflows

backend/test/model-completer.test.ts

@@ -64,7 +64,7 @@ sys.stdout.write(json.dumps({"ok": True, "content": "Descrizione italiana"}))
     signal: new AbortController().signal,
   });
 
-  expect(content).toBe("Descrizione italiana");
+  expect(content).toEqual({ content: "Descrizione italiana", usage: { input: 0, cacheRead: 0, output: 0 } });
   const captured = JSON.parse(readFileSync(join(roots[0]!, "request.json"), "utf8"));
   expect(captured.request).toEqual({
     model: "openai/gpt-4.1-mini",
@@ -100,7 +100,7 @@ sys.stdout.write(json.dumps({"ok": True, "content": "Descrizione Qwen"}))
     },
     messages: [{ role: "user", content: "Describe invented metadata." }],
     signal: new AbortController().signal,
-  })).resolves.toBe("Descrizione Qwen");
+  })).resolves.toEqual({ content: "Descrizione Qwen", usage: { input: 0, cacheRead: 0, output: 0 } });
 
   expect(JSON.parse(readFileSync(join(roots[0]!, "request.json"), "utf8"))).toEqual({
     model: "openai/qwen3.6-35b-a3b",