background-execution

Write and review Swift code that runs work while the app is backgrounded or suspended, choosing the right API for the job and respecting the system's constraints so the work actually runs and the app is not terminated. Review process: 1. Establish the background execution model (lifecycle, budgets, force-quit, the five principles) using `references/fundamentals.md`. 1. Confirm the chosen API matches the work using the decision tree below; reroute if it does not. 1. Validate `BGTaskScheduler` usage (registration timing, Info.plist, expiration, `setTaskCompleted`) using `references/bg-task-scheduler.md`. 1. Validate task assertions (`beginBackgroundTask`/`endBackgroundTask`, `performExpiringActivity`) using `references/task-assertions.md`. 1. Validate background `URLSession` config and the relaunch flow using `references/background-url-session.md`. 1. Validate silent/VoIP push payloads, headers, and handlers using `references/background-push.md`. 1. Validate `UIBackgroundModes` declarations and location specifics using `references/background-modes.md`. 1. Validate background audio (session category, recording while locked, interruptions, route changes, mic permission) using `references/background-audio.md`. 1. Validate SwiftUI `ScenePhase` / `.backgroundTask` usage using `references/swiftui-background-tasks.md`. 1. Validate macOS schedulers (`NSBackgroundActivityScheduler`, `beginActivity`, `SMAppService`) using `references/macos-background.md`. 1. Check testing/debugging and...