HTTP 400
invalid_content_lengthInvalid Content-Length
The MCP request contains an invalid Content-Length header.
Resolution
Send a valid non-negative Content-Length value or let the HTTP client set it.
Response handling
Keep the response's request_id for diagnostics. Retry only transient 429 and 503 responses, using the rate-limit headers and exponential backoff with jitter. Correct 400, 401, and 403 requests before retrying.