Google genai.errors.ClientError with code 400 was being caught and
wrapped as LLMBadRequestError but returned to clients as 502 because
no dedicated FastAPI exception handler existed for LLMBadRequestError.
- Add LLMBadRequestError exception handler in app.py returning HTTP 400
- Fix ErrorCode on Google 400 bad requests from INTERNAL_SERVER_ERROR
to INVALID_ARGUMENT
- Route Google API errors through handle_llm_error in stream_async path
Datadog: https://us5.datadoghq.com/error-tracking/issue/4eb3ff3c-d937-11f0-8177-da7ad0900000🤖 Generated with [Letta Code](https://letta.com)
Co-authored-by: Letta <noreply@letta.com>