Your question is Design a Live Chat System. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Design a live chat system.
Clarify the users, conversation semantics, delivery guarantees, scale, latency objectives, and compliance requirements before proposing an end-to-end design. Address where ML is useful, how online and batch components interact, and how the system behaves during model, network, or dependency failures.