Design Scalable Notification Rate Limiter

Design a production-grade rate limiter for notification sending. The system receives requests for a `user_id` and must decide whether the notification should be sent. Each user belongs to one team, and each team belongs to one company. The service must enforce exact rolling 10-minute limits at three levels: - max **3** accepted notifications per user - max **10** accepted notifications per team - max **20** accepted notifications per company Discuss: - the API and request flow - how to store and query rate-limit state - how to perform an atomic decision across user, team, and company scopes - how to scale to many stateless application servers - how to handle cache misses and changes in the user/team/company hierarchy - hot keys, failures, clock skew, idempotency, and observability Explain the trade-offs in your design.