axiom-cloudkit-ref

# CloudKit Reference

**Purpose**: Comprehensive CloudKit reference for database-based iCloud storage and sync
**Availability**: iOS 10.0+ (basic), iOS 17.0+ (CKSyncEngine), iOS 17.0+ (SwiftData integration)
**Context**: Modern CloudKit sync via CKSyncEngine (WWDC 2023) or SwiftData integration

## When to Use This Skill

Use this skill when:
- Implementing structured data sync to iCloud
- Choosing between SwiftData+CloudKit, CKSyncEngine, or raw CloudKit APIs
- Setting up public/private/shared databases
- Implementing conflict resolution
- Debugging CloudKit sync issues
- Monitoring CloudKit performance

**NOT for**: Simple file sync (use `axiom-icloud-drive-ref` instead)

## Overview

**CloudKit is for STRUCTURED DATA sync** (records with relationships), not simple file sync.

Three modern approaches:
1. **SwiftData + CloudKit** (Easiest, iOS 17+)
2. **CKSyncEngine** (Custom persistence, iOS 17+, WWDC 2023)
3. **Raw CloudKit APIs** (Maximum control, more complexity)

---

## Approach 1: SwiftData + CloudKit (Recommended)

**When to use**: iOS 17+ apps with SwiftData models

**Limitations**:
- Private database only (no public/shared)
- Automatic sync (less control)
- SwiftData constraints apply

```swift
// ✅ CORRECT: SwiftData with CloudKit sync
import SwiftData

@Model
class Task {
    var title: String
    var isCompleted: Bool
    var dueDate: Date

    init(title: String, isCompleted: Bool = false, dueDate: Date) {
        self.title = title
        self.isCompleted = isCompleted
        self.dueDate = dueDate
    }
}

// Configure CloudKit container
let container = try ModelContainer(
    for: Task.self,
    configurations: ModelConfiguration(
        cloudKitDatabase: .private("iCloud.com.example.app")
    )
)

// That's it! Sync happens automatically
```

**Entitlements required**:
- iCloud capability
- CloudKit container

**Use `axiom-swiftdata` skill for SwiftData details**

---

## Approach 2: CKSyncEngine (Modern, WWDC 2023)

**When to use**: Custom per