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Systematic Xcode build performance analysis and optimization. Core principle: Measure before optimizing, then optimize the critical path first.

Core Data issues manifest as production crashes from schema mismatches, mysterious concurrency errors, performance degradation under load, and data corruption from unsafe migrations. Core principle 85% of Core Data problems stem from misunderstanding thread-confinement, schema migration requirements, and relationship query patterns—not Core Data defects.

Systematic diagnosis and resolution of app hangs. A hang occurs when the main thread is blocked for more than 1 second, making the app unresponsive to user input.

Porting OpenGL/OpenGL ES or DirectX code to Metal on Apple platforms.

Core principle: Core Data is a mature object graph and persistence framework. Use it when needing features SwiftData doesn't support, or when targeting older iOS versions.

Purpose: Comprehensive reference for file-based iCloud sync using ubiquitous containers Availability: iOS 5.0+ (basic), iOS 8.0+ (iCloud Drive), iOS 11.0+ (modern APIs) Context: File-based cloud storage, not database (use CloudKit for structured data)

Command-line interface for Instruments profiling. Enables headless performance analysis without GUI.

Purpose: Comprehensive reference for file encryption and data protection APIs Availability: iOS 4.0+ (all protection levels), latest enhancements in iOS 26 Context: Built on iOS Data Protection architecture using hardware encryption

Comprehensive API reference for modern Core Location (iOS 17+).

Apple bundles for-LLM markdown documentation inside Xcode. These are authoritative, up-to-date guides and diagnostics written by Apple engineers. Use them alongside Axiom skills for the most accurate information.