Send a message to the AI chat assistant
message field is required and must be non-empty.conversation_id to continue an existing conversation, or omit it to start a new one.provider field selects an AI model provider; defaults to the platform default when omitted.low_stakes: true for lighter-weight responses where lower latency is preferred over depth.X-Idempotency-Key header to prevent duplicate message processing on retries.{ "result": "success", "data": ... } where data contains the assistant’s reply and conversation metadata.503 if the chat service is not configured or unavailable.