fix(ev): preview EV via software matrix, flush AE bias only at capture

App.tsx

@@ -9,7 +9,7 @@ import * as Haptics from 'expo-haptics';
 import AsyncStorage from '@react-native-async-storage/async-storage';
 
 import TopBar from './src/components/TopBar';
-import Viewfinder from './src/components/Viewfinder';
+import Viewfinder, { type ViewfinderHandle } from './src/components/Viewfinder';
 import AdjustmentPanel from './src/components/AdjustmentPanel';
 import CameraControls from './src/components/CameraControls';
 import ToolRail, { TabId } from './src/components/ToolRail';
@@ -32,6 +32,10 @@ console.error('[camdebug-ver] debug build console.error path');
 
 export default function App() {
   const [mode, setMode] = useState<'camera' | 'library'>('camera');
+  // Imperative handle into the Viewfinder camera controller: flushes the EV to
+  // the hardware AE bias right before each capture (live slider drags never
+  // touch the hardware — that flashed the Xiaomi preview).
+  const viewfinderRef = useRef<ViewfinderHandle>(null);
   const [recipes, setRecipes] = useState<Recipe[]>([]);
   const [selectedRecipe, setSelectedRecipe] = useState<Recipe | null>(null);
   
@@ -393,6 +397,14 @@ export default function App() {
         }
 
         const tShot = Date.now();
+        // Hardware AE bias for this shot (best-effort, bounded retries inside).
+        // Applied here — right before the capture — instead of live during EV
+        // slider drags, which re-locked AE on the Xiaomi and flashed preview.
+        try {
+          await viewfinderRef.current?.flushExposureBias();
+        } catch (e) {
+          console.error('[ev] flush at capture failed: ' + String(e));
+        }
         const { filePath } = await photoOutput.capturePhotoToFile({}, {});
         console.error(`[capture] shot-took ${Date.now() - tShot}ms`);
         const sourceUri = toUri(filePath);
@@ -504,6 +516,7 @@ export default function App() {
       {/* Fullscreen hero: photo or live preview fills the whole screen */}
       <View className="absolute inset-0 bg-black">
         <Viewfinder
+          ref={viewfinderRef}
           mode={mode}
           recipe={
             selectedRecipe || {