In-depth guide to Factory, a container-based dependency injection system for Swift and SwiftUI. Use this skill any time the user is writing, reading, refactoring, debugging, or testing Swift code that uses Factory, FactoryKit, or FactoryTesting — including registrations on Container, the `@Injected`/`@LazyInjected`/`@WeakLazyInjected`/`@DynamicInjected`/`@InjectedObject`/`@InjectedObservable` property wrappers, `Factory<T>` and `ParameterFactory<P, T>`, scopes (`.unique`, `.cached`, `.shared`, `.singleton`, `.graph`), context modifiers (`.onTest`, `.onPreview`, `.onDebug`, `.onArg`, `.onSimulator`, `.onDevice`), `AutoRegistering`, custom containers, the `.container` Swift Testing trait, and cross-module wiring with `promised()`. Trigger when you see `Factory<`, `Container.shared`, `extension Container`, `@Injected(\.`, `import FactoryKit`, or when the user mentions "Factory DI", "FactoryKit", or compares against Resolver, Swinject, or Needle.