Force simulate mode when OSM OAuth secrets are missing

Preview/PR builds don't have access to GitHub Secrets, so the OAuth
client IDs are empty. Previously this caused a runtime crash from
keys.dart throwing on empty values. Now we detect missing secrets
and force simulate mode, which already fully supports fake auth
and uploads.

Also fixes a latent bug where forceLogin() would crash with
LateInitializationError in simulate mode since _helper is never
initialized when OAuth setup is skipped.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/keys.dart

@@ -1,16 +1,20 @@
 // OpenStreetMap OAuth client IDs for this app.
 // These must be provided via --dart-define at build time.
 
+/// Whether OSM OAuth secrets were provided at build time.
+/// When false, the app should force simulate mode.
+bool get kHasOsmSecrets {
+  const prod = String.fromEnvironment('OSM_PROD_CLIENTID');
+  const sandbox = String.fromEnvironment('OSM_SANDBOX_CLIENTID');
+  return prod.isNotEmpty && sandbox.isNotEmpty;
+}
+
 String get kOsmProdClientId {
   const fromBuild = String.fromEnvironment('OSM_PROD_CLIENTID');
-  if (fromBuild.isNotEmpty) return fromBuild;
-  
-  throw Exception('OSM_PROD_CLIENTID not configured. Use --dart-define=OSM_PROD_CLIENTID=your_id');
+  return fromBuild;
 }
 
 String get kOsmSandboxClientId {
   const fromBuild = String.fromEnvironment('OSM_SANDBOX_CLIENTID');
-  if (fromBuild.isNotEmpty) return fromBuild;
-  
-  throw Exception('OSM_SANDBOX_CLIENTID not configured. Use --dart-define=OSM_SANDBOX_CLIENTID=your_id');
+  return fromBuild;
 }

lib/screens/settings/sections/upload_mode_section.dart

@@ -23,6 +23,8 @@ class UploadModeSection extends StatelessWidget {
               subtitle: Text(locService.t('uploadMode.subtitle')),
               trailing: DropdownButton<UploadMode>(
                 value: appState.uploadMode,
+                // This entire section is gated behind kEnableDevelopmentModes
+                // in osm_account_screen.dart, so all modes are always available here.
                 items: [
                   DropdownMenuItem(
                     value: UploadMode.production,

lib/services/auth_service.dart

@@ -36,6 +36,7 @@ class AuthService {
 
   void setUploadMode(UploadMode mode) {
     _mode = mode;
+    if (mode == UploadMode.simulate || !kHasOsmSecrets) return;
     final isSandbox = (mode == UploadMode.sandbox);
     final authBase = isSandbox
       ? 'https://master.apis.dev.openstreetmap.org'
@@ -150,7 +151,9 @@ class AuthService {
 
   // Force a fresh login by clearing stored tokens
   Future<String?> forceLogin() async {
-    await _helper.removeAllTokens();
+    if (_mode != UploadMode.simulate) {
+      await _helper.removeAllTokens();
+    }
     _displayName = null;
     return await login();
   }

lib/state/settings_state.dart

@@ -5,6 +5,7 @@ import 'package:collection/collection.dart';
 
 import '../models/tile_provider.dart';
 import '../dev_config.dart';
+import '../keys.dart';
 
 // Enum for upload mode (Production, OSM Sandbox, Simulate)
 enum UploadMode { production, sandbox, simulate }
@@ -41,7 +42,8 @@ class SettingsState extends ChangeNotifier {
   bool _offlineMode = false;
   bool _pauseQueueProcessing = false;
   int _maxNodes = kDefaultMaxNodes;
-  UploadMode _uploadMode = kEnableDevelopmentModes ? UploadMode.simulate : UploadMode.production;
+  // Default must account for missing secrets (preview builds) even before init() runs
+  UploadMode _uploadMode = (kEnableDevelopmentModes || !kHasOsmSecrets) ? UploadMode.simulate : UploadMode.production;
   FollowMeMode _followMeMode = FollowMeMode.follow;
   bool _proximityAlertsEnabled = false;
   int _proximityAlertDistance = kProximityAlertDefaultDistance;
@@ -150,8 +152,16 @@ class SettingsState extends ChangeNotifier {
       await prefs.setInt(_uploadModePrefsKey, _uploadMode.index);
     }
     
-    // In production builds, force production mode if development modes are disabled
-    if (!kEnableDevelopmentModes && _uploadMode != UploadMode.production) {
+    // Override persisted upload mode when the current build configuration
+    // doesn't support it. This handles two cases:
+    // 1. Preview/PR builds without OAuth secrets — force simulate to avoid crashes
+    // 2. Production builds — force production (prefs may have sandbox/simulate
+    //    from a previous dev build on the same device)
+    if (!kHasOsmSecrets && _uploadMode != UploadMode.simulate) {
+      debugPrint('SettingsState: No OSM secrets available, forcing simulate mode');
+      _uploadMode = UploadMode.simulate;
+      await prefs.setInt(_uploadModePrefsKey, _uploadMode.index);
+    } else if (kHasOsmSecrets && !kEnableDevelopmentModes && _uploadMode != UploadMode.production) {
       debugPrint('SettingsState: Development modes disabled, forcing production mode');
       _uploadMode = UploadMode.production;
       await prefs.setInt(_uploadModePrefsKey, _uploadMode.index);
@@ -258,11 +268,10 @@ class SettingsState extends ChangeNotifier {
   }
 
   Future<void> setUploadMode(UploadMode mode) async {
-    // In production builds, only allow production mode
-    if (!kEnableDevelopmentModes && mode != UploadMode.production) {
-      debugPrint('SettingsState: Development modes disabled, forcing production mode');
-      mode = UploadMode.production;
-    }
+    // The upload mode dropdown is only visible when kEnableDevelopmentModes is
+    // true (gated in osm_account_screen.dart), so no secrets/dev-mode guards
+    // are needed here. The init() method handles forcing the correct mode on
+    // startup for production builds and builds without OAuth secrets.
     
     _uploadMode = mode;
     final prefs = await SharedPreferences.getInstance();

test/state/settings_state_test.dart

@@ -0,0 +1,73 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+import 'package:deflockapp/state/settings_state.dart';
+import 'package:deflockapp/keys.dart';
+
+void main() {
+  setUp(() {
+    SharedPreferences.setMockInitialValues({});
+  });
+
+  group('kHasOsmSecrets (no --dart-define)', () {
+    test('is false when built without secrets', () {
+      expect(kHasOsmSecrets, isFalse);
+    });
+
+    test('client ID getters return empty strings instead of throwing', () {
+      expect(kOsmProdClientId, isEmpty);
+      expect(kOsmSandboxClientId, isEmpty);
+    });
+  });
+
+  group('SettingsState without secrets', () {
+    test('defaults to simulate mode', () {
+      final state = SettingsState();
+      expect(state.uploadMode, UploadMode.simulate);
+    });
+
+    test('init() forces simulate even if prefs has production stored', () async {
+      SharedPreferences.setMockInitialValues({
+        'upload_mode': UploadMode.production.index,
+      });
+
+      final state = SettingsState();
+      await state.init();
+
+      expect(state.uploadMode, UploadMode.simulate);
+
+      // Verify it persisted the override
+      final prefs = await SharedPreferences.getInstance();
+      expect(prefs.getInt('upload_mode'), UploadMode.simulate.index);
+    });
+
+    test('init() forces simulate even if prefs has sandbox stored', () async {
+      SharedPreferences.setMockInitialValues({
+        'upload_mode': UploadMode.sandbox.index,
+      });
+
+      final state = SettingsState();
+      await state.init();
+
+      expect(state.uploadMode, UploadMode.simulate);
+    });
+
+    test('init() keeps simulate if already simulate', () async {
+      SharedPreferences.setMockInitialValues({
+        'upload_mode': UploadMode.simulate.index,
+      });
+
+      final state = SettingsState();
+      await state.init();
+
+      expect(state.uploadMode, UploadMode.simulate);
+    });
+
+    test('setUploadMode() allows simulate', () async {
+      final state = SettingsState();
+      await state.setUploadMode(UploadMode.simulate);
+
+      expect(state.uploadMode, UploadMode.simulate);
+    });
+  });
+}