Design a Read-Once Chat System

Design a chat messaging system where one sender can select multiple recipients at send time, but the message is not a group chat message. Instead, the system creates separate recipient-specific deliveries. Core requirements: - A sender can send the same message to many recipients at once. - Each recipient should only be able to view the message one time. - After a recipient reads the message, that recipient's copy must be deleted or made permanently unavailable. - One recipient reading a message must not affect another recipient's copy. - The system should support online delivery, offline recipients, retries, and large-scale traffic. Please describe: - APIs - data model - high-level architecture - message fan-out strategy - read-once enforcement - deletion and retention behavior - scaling, load balancing, and partitioning choices - failure handling and consistency tradeoffs