Keep screen awake in camera mode; nudge flip button toward shutter

src/components/Viewfinder.tsx

@@ -1,6 +1,7 @@
 import React, { useCallback, useEffect, useMemo, useRef, useState, forwardRef, useImperativeHandle, type ComponentProps } from 'react';
 import { View, Text, StyleSheet, TouchableOpacity, useWindowDimensions, AppState } from 'react-native';
 import { useSafeAreaInsets } from 'react-native-safe-area-context';
+import { activateKeepAwake, deactivateKeepAwake } from 'expo-keep-awake';
 import { useCameraDevice, type CameraPhotoOutput } from 'react-native-vision-camera';
 import { SkiaCamera, type SkiaCameraRef } from 'react-native-vision-camera-skia';
 import { createSynchronizable } from 'react-native-worklets';
@@ -313,6 +314,17 @@ const Viewfinder = forwardRef<ViewfinderHandle, ViewfinderProps>(function Viewfi
     const sub = AppState.addEventListener('change', (s) => setAppActive(s === 'active'));
     return () => sub.remove();
   }, []);
+  // Keep the screen lit while the live camera is showing. Without this the
+  // display sleeps after the system timeout; when the user wakes it much later
+  // (deep idle/doze) the preview surface is gone but the JS AppState never saw
+  // a background event, so the session is never restarted and the viewfinder
+  // (and capture) stay black until the camera is re-mounted (flip/switch).
+  useEffect(() => {
+    if (mode === 'camera') {
+      activateKeepAwake('camera-viewfinder');
+      return () => deactivateKeepAwake('camera-viewfinder');
+    }
+  }, [mode]);
   // Tap-to-focus / AE-AF-AWB lock point (view coords). null = auto continuous.
   const [focusPoint, setFocusPoint] = useState<{ x: number; y: number } | null>(null);
   const controller = cameraActive ? skiaCameraRef.current?.controller : undefined;