feat: section 4 — Android battery optimization prompt

One-time prompt on first launch (Android only) directing the user to
exclude bincio-rec from battery optimization. Uses the direct
REQUEST_IGNORE_BATTERY_OPTIMIZATIONS system dialog with a fallback to
the general settings page for OEMs that block the direct intent.
Dismissal persisted in AsyncStorage so prompt never repeats.

App.tsx

@@ -4,6 +4,7 @@ import * as Notifications from 'expo-notifications';
 import { GestureHandlerRootView } from 'react-native-gesture-handler';
 import { AppNavigator } from './src/navigation/AppNavigator';
 import { requestNotificationPermissions } from './src/services/gps';
+import { promptBatteryOptimizationIfNeeded } from './src/services/batteryOptimization';
 
 // Show notifications even when the app is in the foreground (iOS suppresses by default)
 Notifications.setNotificationHandler({
@@ -18,6 +19,7 @@ Notifications.setNotificationHandler({
 export default function App() {
   useEffect(() => {
     requestNotificationPermissions();
+    promptBatteryOptimizationIfNeeded();
   }, []);
 
   return (

CLAUDE.md

@@ -117,9 +117,9 @@ Items below are what remains before v1 is shippable.
 - [x] **Permission request** — `requestNotificationPermissions()` called in `App.tsx` on mount; foreground notification handler set at module level so iOS shows banners while app is active
 - [x] **Milestone tracker** — module-level `runningDistanceMeters` / `lastNotifiedKm` / `prevPoint` in `gps.ts`, reset on each `startGpsRecording()`; each incoming location adds haversine distance and fires a notification when a new km is crossed, gated on the `kmNotifications` AsyncStorage setting
 
-### 4 — Android battery optimization prompt (1–2 hours)
+### 4 — Android battery optimization prompt ✅
 
-- [ ] On first launch, detect if the app is affected by battery optimization (`expo-intent-launcher`) and show a one-time prompt directing the user to whitelist bincio-rec; persist dismissal in AsyncStorage so it only shows once
+- [x] `src/services/batteryOptimization.ts` — Android-only, one-time prompt (dismissed flag in AsyncStorage); uses `REQUEST_IGNORE_BATTERY_OPTIMIZATIONS` intent to open the system dialog for bincio-rec directly; falls back to `IGNORE_BATTERY_OPTIMIZATION_SETTINGS` (general page) on OEMs that block the direct intent; called from `App.tsx` on mount alongside notification permission request
 
 ### 5 — Map (optional upgrade)
 

src/services/batteryOptimization.ts

@@ -0,0 +1,35 @@
+import { Platform, Alert } from 'react-native';
+import * as IntentLauncher from 'expo-intent-launcher';
+import AsyncStorage from '@react-native-async-storage/async-storage';
+
+const PROMPT_SHOWN_KEY = 'batteryOptPromptShown';
+
+export async function promptBatteryOptimizationIfNeeded(): Promise<void> {
+  if (Platform.OS !== 'android') return;
+
+  const shown = await AsyncStorage.getItem(PROMPT_SHOWN_KEY);
+  if (shown) return;
+
+  await AsyncStorage.setItem(PROMPT_SHOWN_KEY, 'true');
+
+  Alert.alert(
+    'Allow background GPS',
+    'To record accurately while the screen is off, bincio-rec needs to be excluded from battery optimization.\n\nTap "Open settings", find bincio-rec, and select "Don\'t optimize".',
+    [
+      {
+        text: 'Open settings',
+        onPress: () =>
+          IntentLauncher.startActivityAsync(
+            IntentLauncher.ActivityAction.REQUEST_IGNORE_BATTERY_OPTIMIZATIONS,
+            { data: 'package:com.bincio.rec' },
+          ).catch(() =>
+            // Fallback: some OEMs don't support the direct intent — open the general page
+            IntentLauncher.startActivityAsync(
+              IntentLauncher.ActivityAction.IGNORE_BATTERY_OPTIMIZATION_SETTINGS,
+            ),
+          ),
+      },
+      { text: 'Later', style: 'cancel' },
+    ],
+  );
+}