HostedCheckoutRelay

Bridges HostedWebViewGateway.pay (a suspending call with no UI of its own) to the Compose WebView screen that actually renders the checkout and detects the return-URL. One relay instance is shared (Koin single) across every hosted-webview config, keyed by GatewayId rather than single-slot like a per-gateway relay — many configs share this one module.

Flow: HostedWebViewGateway.pay registers a listener and calls launch; whichever composable is observing requests renders the checkout for that gateway and calls reportResult once matchReturn fires; pay resumes with the mapped com.siddharth.kmp.paymentsapi.PaymentResult.