SwiftUI ⇄ UIKit Interop

This skill covers the boundary between SwiftUI and UIKit — embedding one inside the other and passing data across. It does not cover pure-SwiftUI view design (use swiftui-expert) or the app's dependency graph (use ios-architecture-expert).

Agent Behavior Contract

When this skill is active, follow these rules strictly:

1. This skill is only about the boundary. Pure SwiftUI view code → defer to swiftui-expert; app architecture / composition root / DI → defer to ios-architecture-expert.
2. Wrap UIKit in SwiftUI with a representable — UIViewRepresentable for a view, UIViewControllerRepresentable for a view controller. Never new up a UIKit view directly inside a SwiftUI body.
3. Route all UIKit delegate / data-source / target-action callbacks through a Coordinator (makeCoordinator()), never store mutable UIKit state on the representable struct.
4. Data flows one way per direction: SwiftUI state → updateUIView/updateUIViewController; UIKit events → Coordinator → @Binding/closure. Don't mutate SwiftUI state synchronously from inside updateUIView.
5. Embed SwiftUI in UIKit with UIHostingController — and when embedding (not presenting), add it as a child view controller (addChild / didMove(toParent:)), not just its view.
6. Use UIHostingConfiguration for SwiftUI in collection/table cells (iOS 16+) — one configuration per cell, not a UIHostingController per cell.
7. Keep hosting sizing correct — set sizingOptions / honor intrinsicContentSize / safeAreaRegions so Auto Layout and self-sizing cells measure the SwiftUI content.
8. Gate version-specific APIs (UIHostingConfiguration iOS 16, UIHostingController.sizingOptions iOS 16, trait-bridged environment iOS 17, @UIApplicationDelegateAdaptor lifecycle) with #available/@available.