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 code paths?
4. Is work in background handlers minimal (~15 second limit)?
5. Are HKQueryAnchors persisted per sample type (not shared)?