Add on-device debug logging: file capture + share (for real-session testing)

- fileLogger: append redacted API requests/responses + app events to an on-device
  log file (persists across restarts); the client's logSink now writes to it
- Diagnostics screen (Account > Diagnostics): toggle recording, Share log file
  (expo-sharing), clear. StartSession logs the session attempt/result explicitly.
- Lets a real parking session be captured while away from a computer, then shared.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/src/api/client.ts

@@ -3,6 +3,7 @@ import * as Localization from 'expo-localization';
 import { ParkSmarterClient, type EnvironmentName } from 'parksmarter-client';
 import { secureTokenStore } from './secureTokenStore';
 import { authBus } from '@/auth/authBus';
+import { logLine } from '@/features/diagnostics/fileLogger';
 
 const env =
   (Constants.expoConfig?.extra?.psEnvironment as EnvironmentName) ?? 'prodv2';
@@ -17,7 +18,11 @@ export const ps = new ParkSmarterClient({
   tokens: secureTokenStore,
   localeCode: (Localization.getLocales()[0]?.languageCode ?? 'en').toLowerCase(),
   onUnauthorized: () => authBus.onUnauthorized?.(),
-  // Redacted request/response logging -> logcat (grep "PS →" / "PS ←").
-  // Toggle at runtime with ps.setLogRequests(false), or flip extra.debugHttp.
+  // Redacted request/response logging -> logcat AND the on-device log file (when
+  // enabled in Diagnostics). Toggle at runtime with ps.setLogRequests().
   logRequests: Boolean(Constants.expoConfig?.extra?.debugHttp),
+  logSink: (line: string) => {
+    console.log(line);
+    logLine(line);
+  },
 });

app/src/features/diagnostics/fileLogger.ts

@@ -0,0 +1,83 @@
+import * as FileSystem from 'expo-file-system';
+import * as Sharing from 'expo-sharing';
+import AsyncStorage from '@react-native-async-storage/async-storage';
+
+/**
+ * On-device debug log. When enabled, API requests/responses (already redacted by
+ * the client) and app events are appended to a file the user can share afterward
+ * — useful for capturing a real parking-session attempt while away from a computer.
+ */
+const LOG_URI = FileSystem.documentDirectory + 'bbp-debug.log';
+const ENABLED_KEY = 'ps_file_logging';
+const MAX_LINES = 4000;
+
+let enabled = false;
+let buffer: string[] = [];
+let flushTimer: ReturnType<typeof setTimeout> | null = null;
+
+export async function initFileLogging(): Promise<boolean> {
+  enabled = (await AsyncStorage.getItem(ENABLED_KEY)) === 'true';
+  if (enabled) {
+    // Carry over the previous session's log so a crash mid-test isn't lost.
+    try {
+      const info = await FileSystem.getInfoAsync(LOG_URI);
+      if (info.exists) {
+        const prev = await FileSystem.readAsStringAsync(LOG_URI);
+        buffer = prev.split('\n').slice(-MAX_LINES);
+      }
+    } catch {
+      /* ignore */
+    }
+  }
+  return enabled;
+}
+
+export function isFileLoggingEnabled(): boolean {
+  return enabled;
+}
+
+export async function setFileLogging(on: boolean): Promise<void> {
+  enabled = on;
+  await AsyncStorage.setItem(ENABLED_KEY, String(on));
+  if (on) logLine('--- logging enabled ---');
+  else await flush();
+}
+
+export function logLine(line: string): void {
+  if (!enabled) return;
+  buffer.push(`${new Date().toISOString()} ${line}`);
+  if (buffer.length > MAX_LINES) buffer = buffer.slice(-MAX_LINES);
+  if (flushTimer) clearTimeout(flushTimer);
+  flushTimer = setTimeout(() => void flush(), 1200);
+}
+
+export async function flush(): Promise<void> {
+  try {
+    await FileSystem.writeAsStringAsync(LOG_URI, buffer.join('\n'));
+  } catch {
+    /* ignore */
+  }
+}
+
+export async function shareLog(): Promise<void> {
+  await flush();
+  if (await Sharing.isAvailableAsync()) {
+    await Sharing.shareAsync(LOG_URI, {
+      mimeType: 'text/plain',
+      dialogTitle: 'BigBrainParking debug log',
+    });
+  }
+}
+
+export async function clearLog(): Promise<void> {
+  buffer = [];
+  try {
+    await FileSystem.deleteAsync(LOG_URI, { idempotent: true });
+  } catch {
+    /* ignore */
+  }
+}
+
+export function logStats(): { lines: number } {
+  return { lines: buffer.length };
+}

app/src/navigation/RootNavigator.tsx

@@ -21,6 +21,7 @@ import { VehiclesScreen } from '@/screens/VehiclesScreen';
 import { PaymentMethodsScreen } from '@/screens/PaymentMethodsScreen';
 import { NotificationsScreen } from '@/screens/NotificationsScreen';
 import { StartSessionScreen } from '@/screens/StartSessionScreen';
+import { DiagnosticsScreen } from '@/screens/DiagnosticsScreen';
 import { useTheme } from '@/theme/ThemeContext';
 import type { Zone } from 'parksmarter-client';
 
@@ -33,6 +34,7 @@ export type RootStackParamList = {
   Vehicles: undefined;
   PaymentMethods: undefined;
   Notifications: undefined;
+  Diagnostics: undefined;
 };
 
 export type TabParamList = {
@@ -131,6 +133,11 @@ export function RootNavigator() {
             component={NotificationsScreen}
             options={{ title: 'Notifications' }}
           />
+          <Stack.Screen
+            name="Diagnostics"
+            component={DiagnosticsScreen}
+            options={{ title: 'Diagnostics' }}
+          />
         </Stack.Navigator>
       ) : (
         <LoginScreen />

app/src/screens/AccountScreen.tsx

@@ -1,10 +1,8 @@
-import React, { useState } from 'react';
+import React from 'react';
 import { ScrollView, StyleSheet, Switch, Text, TouchableOpacity, View } from 'react-native';
-import Constants from 'expo-constants';
 import { Ionicons } from '@expo/vector-icons';
 import { useNavigation } from '@react-navigation/native';
 import type { NativeStackNavigationProp } from '@react-navigation/native-stack';
-import { ps } from '@/api/client';
 import { useAuth } from '@/auth/AuthContext';
 import { useTheme } from '@/theme/ThemeContext';
 import type { RootStackParamList } from '@/navigation/RootNavigator';
@@ -15,9 +13,6 @@ export function AccountScreen() {
   const { colors, mode, toggle } = useTheme();
   const { logout } = useAuth();
   const navigation = useNavigation<Nav>();
-  const [logging, setLogging] = useState<boolean>(
-    Boolean(Constants.expoConfig?.extra?.debugHttp),
-  );
 
   const Item = ({
     icon,
@@ -63,17 +58,7 @@ export function AccountScreen() {
           <Text style={[styles.itemText, { color: colors.text }]}>Dark mode</Text>
           <Switch value={mode === 'dark'} onValueChange={toggle} />
         </View>
-        <View style={[styles.item, { borderBottomColor: colors.border }]}>
-          <Ionicons name="bug" size={20} color={colors.primary} />
-          <Text style={[styles.itemText, { color: colors.text }]}>Log requests (debug)</Text>
-          <Switch
-            value={logging}
-            onValueChange={(v) => {
-              setLogging(v);
-              ps.setLogRequests(v);
-            }}
-          />
-        </View>
+        <Item icon="bug" label="Diagnostics" onPress={() => navigation.navigate('Diagnostics')} />
       </View>
 
       <TouchableOpacity

app/src/screens/DiagnosticsScreen.tsx

@@ -0,0 +1,96 @@
+import React, { useCallback, useState } from 'react';
+import { Alert, StyleSheet, Switch, Text, TouchableOpacity, View } from 'react-native';
+import { useFocusEffect } from '@react-navigation/native';
+import { ps } from '@/api/client';
+import { useTheme } from '@/theme/ThemeContext';
+import {
+  clearLog,
+  isFileLoggingEnabled,
+  logStats,
+  setFileLogging,
+  shareLog,
+} from '@/features/diagnostics/fileLogger';
+
+export function DiagnosticsScreen() {
+  const { colors } = useTheme();
+  const [on, setOn] = useState(false);
+  const [lines, setLines] = useState(0);
+
+  useFocusEffect(
+    useCallback(() => {
+      setOn(isFileLoggingEnabled());
+      setLines(logStats().lines);
+    }, []),
+  );
+
+  const toggle = async (v: boolean) => {
+    setOn(v);
+    await setFileLogging(v);
+    ps.setLogRequests(v);
+    setLines(logStats().lines);
+  };
+
+  return (
+    <View style={[styles.container, { backgroundColor: colors.bg }]}>
+      <View style={[styles.card, { backgroundColor: colors.card }]}>
+        <View style={styles.row}>
+          <View style={{ flex: 1 }}>
+            <Text style={[styles.title, { color: colors.text }]}>Record debug log</Text>
+            <Text style={[styles.sub, { color: colors.subtext }]}>
+              Saves API requests/responses and app events to a file on this device.
+              Sensitive values (tokens, card numbers) are redacted.
+            </Text>
+          </View>
+          <Switch value={on} onValueChange={toggle} />
+        </View>
+      </View>
+
+      <Text style={[styles.count, { color: colors.subtext }]}>
+        {lines} line{lines === 1 ? '' : 's'} captured
+      </Text>
+
+      <TouchableOpacity
+        style={[styles.btn, { backgroundColor: colors.primary }]}
+        onPress={() => shareLog().catch((e) => Alert.alert('Share failed', String(e?.message ?? e)))}
+      >
+        <Text style={styles.btnText}>Share log file</Text>
+      </TouchableOpacity>
+
+      <TouchableOpacity
+        style={[styles.btn, { backgroundColor: colors.card, borderWidth: 1, borderColor: colors.border }]}
+        onPress={() =>
+          Alert.alert('Clear log?', 'Deletes the captured log.', [
+            { text: 'Cancel', style: 'cancel' },
+            {
+              text: 'Clear',
+              style: 'destructive',
+              onPress: async () => {
+                await clearLog();
+                setLines(0);
+              },
+            },
+          ])
+        }
+      >
+        <Text style={[styles.btnText, { color: colors.text }]}>Clear log</Text>
+      </TouchableOpacity>
+
+      <Text style={[styles.note, { color: colors.subtext }]}>
+        Turn this on before heading out, do your parking session, then come back and
+        “Share log file” to send it to yourself. It persists across app restarts.
+      </Text>
+    </View>
+  );
+}
+
+const styles = StyleSheet.create({
+  container: { flex: 1, padding: 16 },
+  card: { borderRadius: 12, padding: 16 },
+  row: { flexDirection: 'row', alignItems: 'center' },
+  title: { fontSize: 16, fontWeight: '600' },
+  sub: { fontSize: 13, marginTop: 4, lineHeight: 18 },
+  count: { fontSize: 13, marginTop: 16, marginLeft: 4 },
+  btn: { borderRadius: 12, padding: 16, alignItems: 'center', marginTop: 12 },
+  btnText: { color: '#fff', fontWeight: '700', fontSize: 16 },
+  note: { fontSize: 12, marginTop: 20, lineHeight: 18 },
+});

app/src/screens/StartSessionScreen.tsx

@@ -15,6 +15,7 @@ import type { NativeStackNavigationProp } from '@react-navigation/native-stack';
 import { ps } from '@/api/client';
 import { useTheme } from '@/theme/ThemeContext';
 import { scheduleExpiryReminder } from '@/notifications/localReminders';
+import { logLine } from '@/features/diagnostics/fileLogger';
 import type { RootStackParamList } from '@/navigation/RootNavigator';
 import type {
   CreditCardDetail,
@@ -142,6 +143,11 @@ export function StartSessionScreen() {
   const doStart = async () => {
     if (!selected) return;
     setPaying(true);
+    logLine(
+      `[SESSION] start attempt zone=${zone.ZoneName} space=${space?.SpaceId} vehicle=${vehicleId} ` +
+        `card=${cardId} min=${selected.Minutes} cost=${selected.ParkingCost} fee=${selected.TransactionFee} ` +
+        `start="${selected.StartTime}" end="${selected.EndTime}"`,
+    );
     try {
       const res = await ps.startParkingSession({
         creditCardId: cardId!,
@@ -166,10 +172,12 @@ export function StartSessionScreen() {
           endTime: end,
         });
       }
+      logLine(`[SESSION] start OK: ${JSON.stringify(res)}`);
       Alert.alert('Parked!', `Session started at ${zone.ZoneName}.`, [
         { text: 'OK', onPress: () => navigation.navigate('Tabs') },
       ]);
     } catch (e: any) {
+      logLine(`[SESSION] start FAILED: ${e?.status ?? ''} ${e?.serverMessage ?? e?.message ?? e}`);
       Alert.alert('Could not start session', e?.serverMessage ?? e?.message ?? 'error');
     } finally {
       setPaying(false);