watchos-code-review

# watchOS Code Review

## Quick Reference

| Issue Type | Reference |
|------------|-----------|
| App lifecycle, scenes, background modes, extended runtime | [references/lifecycle.md](references/lifecycle.md) |
| ClockKit, WidgetKit, timeline providers, Smart Stack | [references/complications.md](references/complications.md) |
| WCSession, message passing, file transfer, reachability | [references/connectivity.md](references/connectivity.md) |
| Memory limits, background refresh, battery optimization | [references/performance.md](references/performance.md) |

## Review Checklist

- [ ] SwiftUI App protocol used with `@WKApplicationDelegateAdaptor` for lifecycle events
- [ ] `scenePhase` read from root view (not sheets/modals where it's always `.active`)
- [ ] `WKExtendedRuntimeSession` started only while app is active (not from background)
- [ ] Workout sessions recovered in `applicationDidFinishLaunching` (not just delegate)
- [ ] Background tasks scheduled at least 5 minutes apart; next scheduled before completing current
- [ ] `URLSessionDownloadTask` (not `DataTask`) used for background network requests
- [ ] WidgetKit used instead of ClockKit for watchOS 9+ complications
- [ ] Timeline includes future entries (not just current state); gaps avoided
- [ ] `TimelineEntryRelevance` implemented for Smart Stack prioritization
- [ ] WCSession delegate set before `activate()`; singleton pattern used
- [ ] `isReachable` checked before `sendMessage`; `transferUserInfo` for critical data
- [ ] Received files moved synchronously before delegate callback returns

## When to Load References

- Reviewing app lifecycle, background modes, or extended sessions -> lifecycle.md
- Reviewing complications, widgets, or timeline providers -> complications.md
- Reviewing WCSession, iPhone-Watch communication -> connectivity.md
- Reviewing memory, battery, or performance issues -> performance.md

## Review Questions

1. Is the app using modern SwiftUI lifecycle with delegate adaptor?
2. Are background tasks completing properly (calling `setTaskCompletedWithSnapshot`)?
3. Is UI update frequency reduced when `isLuminanceReduced` is true?
4. Are WatchConnectivity delegate callbacks dispatching to main thread?
5. Is `TabView` nested within another `TabView`? (Memory leak on watchOS)