Axiom Swiftdata Migration

When SwiftData's automatic lightweight migrations aren't enough and you need to handle complex model changes, this skill walks you through the custom migration process. The core insight here is critical: willMigrate only sees your old models, didMigrate only sees new ones, and you can never access both simultaneously. That constraint fundamentally shapes how you architect migrations. The documentation appears focused on iOS 17+ basics while targeting iOS 26+ features, which is a slightly odd split. With 945 GitHub stars and clean security audits, it's clearly being used in production. Worth having on hand before you're desperately Googling SwiftData migration errors at 2am.