iOS Data & Persistence Router
You MUST use this skill for ANY data persistence, database, axiom-storage, CloudKit, or serialization work.
When to Use
Use this router when working with:
- Databases (SwiftData, Core Data, GRDB, SQLiteData)
- Schema migrations
- CloudKit sync
- File storage (iCloud Drive, local storage)
- Data serialization (Codable, JSON)
- Storage strategy decisions
- Keychain / secure credential storage
- Encryption, signing, key management (CryptoKit)
Routing Logic
SwiftData
Working with SwiftData → /skill axiom-swiftdata Schema migration → /skill axiom-swiftdata-migration Migration issues → /skill axiom-swiftdata-migration-diag Migrating from Realm → /skill axiom-realm-migration-ref SwiftData vs SQLiteData → /skill axiom-sqlitedata-migration
Other Databases
GRDB queries → /skill axiom-grdb SQLiteData → /skill axiom-sqlitedata Advanced SQLiteData → /skill axiom-sqlitedata-ref Core Data patterns → /skill axiom-core-data Core Data issues → /skill axiom-core-data-diag
Migrations
Database migration safety → /skill axiom-database-migration (critical - prevents data loss)
Serialization
Codable issues → /skill axiom-codable
Cloud Storage
Cloud sync patterns → /skill axiom-cloud-sync CloudKit → /skill axiom-cloudkit-ref iCloud Drive → /skill axiom-icloud-drive-ref Cloud sync errors → /skill axiom-cloud-sync-diag
Keychain & Encryption
Keychain / secure credential storage → /skill axiom-keychain Keychain errors → /skill axiom-keychain-diag Keychain API reference → /skill axiom-keychain-ref Encryption / signing / key management → /skill axiom-cryptokit CryptoKit API reference → /skill axiom-cryptokit-ref
File Storage
Storage strategy → /skill axiom-storage Storage issues → /skill axiom-storage-diag Storage management → /skill axiom-storage-management-ref File protection → /skill axiom-file-protection-ref
tvOS Storage
tvOS data persistence → /skill axiom-tvos (CRITICAL: no persistent local storage on tvOS) tvOS + CloudKit → /skill axiom-sqlitedata (recommended: SyncEngine as persistent store)
Automated Scanning
Core Data audit → Launch core-data-auditor agent or /axiom:audit core-data (migration risks, thread-confinement, N+1 queries, production data loss) Codable audit → Launch codable-auditor agent or /axiom:audit codable (try? swallowing errors, JSONSerialization, date handling) iCloud audit → Launch icloud-auditor agent or /axiom:audit icloud (entitlement checks, file coordination, CloudKit anti-patterns) Storage audit → Launch storage-auditor agent or /axiom:audit storage (wrong file locations, missing backup exclusions, data loss risks) Database schema audit → Launch database-schema-auditor agent or /axiom:audit database-schema (unsafe ALTER TABLE, DROP operations, missing idempotency, foreign key misuse) SwiftData audit → Launch swiftdata-auditor agent or /axiom:audit swiftdata (struct models, missing VersionedSchema, relationship defaults, background context misuse, N+1 patterns)
Decision Tree
- SwiftData? → swiftdata, swiftdata-migration
- Core Data? → core-data, core-data-diag
- GRDB? → grdb
- SQLiteData? → sqlitedata, sqlitedata-ref
- ANY schema migration? → database-migration (ALWAYS — prevents data loss)
- Realm migration? → realm-migration-ref
- SwiftData vs SQLiteData? → sqlitedata-migration
- Cloud sync architecture? → cloud-sync
- CloudKit? → cloudkit-ref
- iCloud Drive? → icloud-drive-ref
- Cloud sync errors? → cloud-sync-diag
- Codable/JSON serialization? → codable
- File storage strategy? → storage, storage-diag, storage-management-ref
- File protection? → file-protection-ref
- Keychain / storing tokens, passwords, secrets securely? → keychain, keychain-diag, keychain-ref
- SecItem errors (errSecDuplicateItem, errSecItemNotFound, errSecInteractionNotAllowed)? → keychain-diag
- Encryption, signing, Secure Enclave, CryptoKit? → cryptokit, cryptokit-ref
- Quantum-secure cryptography, HPKE, ML-KEM? → cryptokit
- Want Core Data safety scan? → core-data-auditor (Agent)
- Want Codable anti-pattern scan? → codable-auditor (Agent)
- Want iCloud sync audit? → icloud-auditor (Agent)
- Want storage location audit? → storage-auditor (Agent)
- Want database schema/migration safety scan? → database-schema-auditor (Agent)
- Want SwiftData code audit? → swiftdata-auditor (Agent)
- tvOS data persistence? → axiom-tvos (CRITICAL: no persistent local storage) + axiom-sqlitedata (CloudKit SyncEngine)
Anti-Rationalization
| Thought | Reality |
|---|---|
| "Just adding a column, no migration needed" | Schema changes without migration crash users. database-migration prevents data loss. |
| "I'll handle the migration manually" | Manual migrations miss edge cases. database-migration covers rollback and testing. |
| "Simple query, I don't need the skill" | Query patterns prevent N+1 and thread-safety issues. The skill has copy-paste solutions. |
| "CloudKit sync is straightforward" | CloudKit has 15+ failure modes. cloud-sync-diag diagnoses them systematically. |
| "I know Codable well enough" | Codable has silent data loss traps (try? swallows errors). codable skill prevents production bugs. |
| "I'll use local storage on tvOS" | tvOS has NO persistent local storage. System deletes Caches at any time. axiom-tvos explains the iCloud-first pattern. |
| "UserDefaults is fine for this token" | UserDefaults is unencrypted, backed up to iCloud, and visible to MDM profiles. One audit catches it. keychain stores tokens securely. |
| "I'll encrypt it myself with CommonCrypto" | CryptoKit replaced CommonCrypto's buffer-management nightmares with one-line APIs. cryptokit prevents misuse. |
Critical Pattern: Migrations
ALWAYS invoke /skill axiom-database-migration when adding/modifying database columns.
This prevents:
- "FOREIGN KEY constraint failed" errors
- "no such column" crashes
- Data loss from unsafe migrations
Example Invocations
User: "I need to add a column to my SwiftData model" → Invoke: /skill axiom-database-migration (critical - prevents data loss)
User: "How do I query SwiftData with complex filters?" → Invoke: /skill axiom-swiftdata
User: "CloudKit sync isn't working" → Invoke: /skill axiom-cloud-sync-diag
User: "Should I use SwiftData or SQLiteData?" → Invoke: /skill axiom-sqlitedata-migration
User: "Check my Core Data code for safety issues" → Invoke: core-data-auditor agent
User: "Scan for Codable anti-patterns before release" → Invoke: codable-auditor agent
User: "Audit my iCloud sync implementation" → Invoke: icloud-auditor agent
User: "Check if my files are stored in the right locations" → Invoke: storage-auditor agent
User: "Audit my database migrations for safety" → Invoke: database-schema-auditor agent
User: "Check my SwiftData models for issues" → Invoke: swiftdata-auditor agent
User: "How do I persist data on tvOS?" → Invoke: /skill axiom-tvos + /skill axiom-sqlitedata
User: "My tvOS app loses data between launches" → Invoke: /skill axiom-tvos
User: "How do I store an auth token securely?" → Invoke: /skill axiom-keychain
User: "errSecDuplicateItem but I checked and the item doesn't exist" → Invoke: /skill axiom-keychain-diag
User: "How do I encrypt data with AES in Swift?" → Invoke: /skill axiom-cryptokit
User: "I need to sign data with the Secure Enclave" → Invoke: /skill axiom-cryptokit
User: "What's ML-KEM and should I use it?" → Invoke: /skill axiom-cryptokit