text: Title: context_length_exceeded error
  Body: I think the message history keeps building up when running the agent over a large loop like:
  
  ```
  for keyword in keywords:
      result = lead_generation_agent.run_sync(user_promt, deps=keyword)
  ```
  
  because the first iteration runs just fine but after dozen I get this error, why and how can I fix it?
  
  
    File "/Users/UA/.venv/lib/python3.13/site-packages/openai/_base_client.py", line 1638, in _request
      raise self._make_status_error_from_response(err.response) from None
  openai.OpenAIError: Error code: 400 - {'error': {'message': "This model's maximum context length is 128000 tokens. However, your messages resulted in 136707 tokens (136367 in the messages, 340 in the functions). Please reduce the length of the messages or functions.", 'type': 'invalid_request_error', 'param': 'messages', 'code': 'context_length_exceeded'}}
  
  How `Agent` class works, why does it pass the history messages to the next iteration of the for loop?