fix(connection): stop ERR_UNKNOWN_URL_SCHEME when opening app deep links on mobile

Telegram bug #654272: opening the connection app link (immediate-open / connect button)
showed a full-page net::ERR_UNKNOWN_URL_SCHEME on Android and silently failed on iOS, while
working on desktop.

Cause: a programmatic top-level navigation to a custom scheme (happ://, v2rayng://, …) via
window.location.href is rendered as a full-page error inside in-app WebViews (Telegram/Yandex)
on Android and does nothing on iOS — also wiping the fallback UI.

Add openAppScheme(): http(s) navigate normally; custom schemes launch via a hidden, contained
iframe so a failed launch never replaces the page — the app opens if installed, otherwise the
manual 'Open app' link stays usable (a user tap is the reliable trigger). Applied in
DeepLinkRedirect.tsx, Connection.tsx and the static public/miniapp/redirect.html (which now
also surfaces the manual button immediately instead of after 2s).

src/pages/Connection.tsx

@@ -8,6 +8,7 @@ import { useTelegramSDK } from '../hooks/useTelegramSDK';
 import { useHaptic } from '@/platform';
 import { SettingsIcon } from '@/components/icons';
 import { resolveTemplate, hasTemplates } from '../utils/templateEngine';
+import { openAppScheme } from '../utils/openAppScheme';
 import { isHappCryptolinkMode, resolveConnectionUrlForUi } from '../utils/connectionLink';
 import { useAuthStore } from '../store/auth';
 import type { AppConfig, RemnawavePlatformData } from '../types';
@@ -133,8 +134,11 @@ export default function Connection() {
         }
       }
 
-      // In regular browsers open deeplink directly (without intermediate redirect page).
-      window.location.href = resolved;
+      // In regular browsers open the deeplink directly. openAppScheme uses a contained
+      // iframe for custom schemes so an unresolved scheme doesn't paint a full-page
+      // net::ERR_UNKNOWN_URL_SCHEME (Android) / silently fail (iOS); http(s) links
+      // still navigate normally. (Telegram bug #654272.)
+      openAppScheme(resolved);
     },
     [isTelegramWebApp, i18n.language, resolveUrl, connectionLink?.connect_mode, qrConnectionUrl],
   );

src/pages/DeepLinkRedirect.tsx

@@ -4,6 +4,7 @@ import { useTranslation } from 'react-i18next';
 import { useQuery } from '@tanstack/react-query';
 import { brandingApi } from '../api/branding';
 import { copyToClipboard } from '../utils/clipboard';
+import { openAppScheme } from '../utils/openAppScheme';
 import {
   CheckIcon,
   CopyIcon,
@@ -97,10 +98,12 @@ export default function DeepLinkRedirect() {
   const appName = appInfo?.name || appParam || 'VPN';
   const appIcon = appInfo?.icon || appName[0]?.toUpperCase() || 'V';
 
-  // Open deep link - same as miniapp, just window.location.href
+  // Open deep link via a contained iframe attempt so a custom scheme the in-app
+  // WebView can't resolve doesn't replace this page with net::ERR_UNKNOWN_URL_SCHEME
+  // (Android) / silently fail (iOS) and wipe the fallback UI. See openAppScheme.
   const openDeepLink = useCallback(() => {
     if (!deepLink || !isValidDeepLink(deepLink)) return;
-    window.location.href = deepLink;
+    openAppScheme(deepLink);
   }, [deepLink]);
 
   // Countdown timer effect

src/utils/openAppScheme.ts

@@ -0,0 +1,39 @@
+/**
+ * Launch a custom-scheme app deep link (happ://, v2rayng://, vless://, …) without
+ * crashing the page inside in-app browsers.
+ *
+ * Why not `window.location.href = scheme`: a programmatic top-level navigation to a
+ * scheme the WebView can't resolve renders a full-page error — on Android in-app
+ * browsers (Telegram/Yandex/…) `net::ERR_UNKNOWN_URL_SCHEME`, on iOS it silently does
+ * nothing — which destroys the fallback UI (Telegram bug #654272). A hidden <iframe>
+ * navigation is contained: if the app is installed the OS intercepts it; if not, the
+ * failure stays inside the (invisible) frame and our page — with its manual "Open app"
+ * link — survives so the user can tap it (a real user gesture is the reliable trigger).
+ *
+ * http(s) links are normal navigations and are passed straight to location.href.
+ */
+export function openAppScheme(url: string): void {
+  const isHttp = /^https?:\/\//i.test(url);
+  if (isHttp) {
+    window.location.href = url;
+    return;
+  }
+
+  try {
+    const iframe = document.createElement('iframe');
+    iframe.style.display = 'none';
+    iframe.src = url;
+    document.body.appendChild(iframe);
+    window.setTimeout(() => {
+      try {
+        iframe.remove();
+      } catch {
+        /* already detached */
+      }
+    }, 2000);
+  } catch {
+    // iframe creation blocked (very old/locked-down WebView) — fall back to direct
+    // navigation. Worst case this shows the same error the iframe avoided, never worse.
+    window.location.href = url;
+  }
+}