feat(mobile): AuthProvider + crypto-backend registration; drop sharedSmoke canary

apps/mobile/app/_layout.tsx

@@ -1,33 +1,32 @@
+import { crypto } from '@chat-app/shared';
 import { Stack } from 'expo-router';
 import { StatusBar } from 'expo-status-bar';
 import { GestureHandlerRootView } from 'react-native-gesture-handler';
 import { SafeAreaProvider } from 'react-native-safe-area-context';
 
 import { ErrorBoundary } from '../components/ErrorBoundary';
+import { AuthProvider } from '../lib/authContext';
+import { createLibsodiumBackend } from '../lib/cryptoBackend';
 
-// Force-resolve @chat-app/shared at boot so Metro packaging issues
-// surface during the very first dev-client load instead of mid-Phase-1.
-// Reference the export so tree-shaking can't drop it.
-import { sharedSmoke } from '../lib/sharedSmoke';
-void sharedSmoke;
+// Register the crypto backend exactly once, before any code that calls
+// crypto.getCryptoBackend(). Doing it at module load (not inside the
+// component) avoids a race where a child component renders before the
+// effect fires.
+crypto.setCryptoBackend(createLibsodiumBackend());
 
-// Root layout for every Expo Router screen. Provider stack order:
-//   GestureHandlerRootView  — required by gesture-driven libs (BottomSheet,
-//                             swipeable rows, drawer nav). Must be the
-//                             outermost so gesture state is global.
-//   SafeAreaProvider        — feeds notch / status-bar insets to children.
-//   ErrorBoundary           — last line of defence for render errors.
-//   Stack                   — Expo Router's screen registry.
 export default function RootLayout() {
   return (
     <GestureHandlerRootView style={{ flex: 1 }}>
       <SafeAreaProvider>
         <ErrorBoundary>
-          <StatusBar style="auto" />
-          <Stack screenOptions={{ headerShown: false }}>
-            <Stack.Screen name="index" />
-            <Stack.Screen name="(app)" />
-          </Stack>
+          <AuthProvider>
+            <StatusBar style="auto" />
+            <Stack screenOptions={{ headerShown: false }}>
+              <Stack.Screen name="index" />
+              <Stack.Screen name="(app)" />
+              <Stack.Screen name="auth/callback" />
+            </Stack>
+          </AuthProvider>
         </ErrorBoundary>
       </SafeAreaProvider>
     </GestureHandlerRootView>