The WKWebView Frontend
The primary iOS UI is a WKWebView (WebViewController) that renders the Home Assistant web frontend; native Swift code wraps it with platform integrations. WebViewController functionality is spread across many WebViewController+*.swift extension files (navigation, gestures, alerts, URL loading, etc.). Native features communicate with the web UI via a JavaScript message bus handled by WebViewExternalMessageHandler (messages typed as WebViewExternalBusMessage / WebViewExternalBusOutgoingMessage in Sources/App/Frontend/ExternalMessageBus/) and custom URL schemes / deep links defined in AppConstants.