Push Notifications and Background Processing Questions

Designing reliable push notification and background processing systems for mobile devices, taking into account device constraints, operating system behavior, and battery and network optimizations. Topics include notification types and delivery semantics on Apple iOS and Google Android platforms, differences between user visible notifications and silent or background notifications, platform delivery services such as the Apple Push Notification Service and Firebase Cloud Messaging, device token management, permission and opt in considerations, payload size and format limits, notification channels and priority settings, and background work scheduling and restrictions. Architectural concerns covered include end to end delivery pipelines, message queuing, fan out strategies, batching, retry and backoff policies, deduplication, rate limiting, telemetry and monitoring, handling offline devices and collapse keys, privacy and security of notification content, integration with mobile backend systems, and scaling considerations for high throughput and low latency delivery.