Queue Pending Message
Queue a message for delivery when conversation becomes ready.
This endpoint allows users to submit messages even when the conversation’s WebSocket connection is not yet established. Messages are stored server-side and delivered automatically when the conversation transitions to READY status.
Args: conversation_id: The conversation ID (can be task ID before conversation is ready) request: The FastAPI request containing message content
Returns: PendingMessageResponse with the message ID and queue position
Raises: HTTPException 400: If the request body is invalid HTTPException 429: If too many pending messages are queued (limit: 10)

