healthkit-code-review

# HealthKit Code Review

## Quick Reference

| Issue Type | Reference |
|------------|-----------|
| HKHealthStore, permissions, status checks, privacy | [references/authorization.md](references/authorization.md) |
| HKQuery types, predicates, anchored queries, statistics | [references/queries.md](references/queries.md) |
| Background delivery, observer queries, completion handlers | [references/background.md](references/background.md) |
| HKQuantityType, HKCategoryType, workouts, units | [references/data-types.md](references/data-types.md) |

## Review Checklist

- [ ] `HKHealthStore.isHealthDataAvailable()` called before any HealthKit operations
- [ ] Authorization requested only for needed data types (minimal permissions)
- [ ] `requestAuthorization` completion handler not misinterpreted as permission granted
- [ ] No attempt to determine read permission status (privacy by design)
- [ ] Query results dispatched to main thread for UI updates
- [ ] `HKObjectQueryNoLimit` used only with bounded predicates
- [ ] `HKStatisticsQuery` used for aggregations instead of manual summing
- [ ] Observer query `completionHandler()` always called (use `defer`)
- [ ] Background delivery registered in `application(_:didFinishLaunchingWithOptions:)`
- [ ] Background delivery entitlement added (iOS 15+)
- [ ] Correct units used for quantity types (e.g., `count/min` for heart rate)
- [ ] Long-running queries stored as properties and stopped in `deinit`

## When to Load References

- Reviewing authorization/permissions flow -> authorization.md
- Reviewing HKSampleQuery, HKAnchoredObjectQuery, or predicates -> queries.md
- Reviewing HKObserverQuery or `enableBackgroundDelivery` -> background.md
- Reviewing HKQuantityType, HKCategoryType, or HKWorkout -> data-types.md

## Review Questions

1. Is `isHealthDataAvailable()` checked before creating HKHealthStore?
2. Does the code gracefully handle denied permissions (empty results)?
3. Are observer query completion handlers called in all co