{
  "sessions": [
    {
      "sessionKey": "mixed-bob",
      "conversations": [
        [
          { "role": "user",      "content": "测试 mixed timestamp 是否被检测", "timestamp": 1700000000000 },
          { "role": "assistant", "content": "这一条故意没有 timestamp" }
        ]
      ]
    }
  ]
}