Use when building or reviewing SwiftUI UI in a touchstone repo — declarative views, the Observation framework for state, navigation, in-view concurrency, identity/perf, and the a11y/test surface. Triggers on SwiftUI views, `.swift` files declaring `: View`/`some View`, `@Observable`, `@State`/`@Bindable`, `NavigationStack`, `#Preview`. Boundary: Swift-language rules (concurrency, optionals, value types, packages) → swift skill; this layers on top.
