feat: post-onboarding login screen (Google primary, anonymous quiet path)

RootGate gains a login phase between name and shell, keyed on AppController.needsLogin; returning signed-in users skip it. FakeAuthService moved to test/fakes.dart.

app/lib/main.dart

@@ -42,7 +42,7 @@ Future<void> main() async {
   final highlightStore = await HighlightStore.open();
   final api = ApiClient(baseUrl: await ApiClient.resolveBaseUrl(store: store), store: store);
   final repository = CardRepository(api: api, store: store);
-  final appController = AppController(store);
+  final appController = AppController(store, authService);
   final localAi = GemmaLocalAiService(store: store);
   FlutterNativeSplash.remove();
   runApp(CachyApp(

app/lib/ui/core/app_controller.dart

@@ -4,14 +4,39 @@
 /// the app presents itself.
 library;
 
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 
+import '../../data/services/auth_service.dart';
 import '../../data/services/local_store.dart';
 
 class AppController extends ChangeNotifier {
-  AppController(this._store) : _themeMode = _decode(_store.themeMode);
+  AppController(this._store, this._auth)
+      : _themeMode = _decode(_store.themeMode),
+        _authUser = _auth.currentUser {
+    _authSub = _auth.userChanges.listen((u) {
+      _authUser = u;
+      notifyListeners();
+    });
+  }
 
   final LocalStore _store;
+  final AuthService _auth;
+  late final StreamSubscription<AuthUser?> _authSub;
+
+  AuthUser? _authUser;
+
+  /// The current Firebase identity (uid = backend owner_id), or null when
+  /// signed out. Drives the login gate and the profile account section.
+  AuthUser? get authUser => _authUser;
+
+  /// True once the user has cleared onboarding + name but has no Firebase
+  /// identity yet — the one moment [RootGate] shows the login screen.
+  bool get needsLogin => seenOnboarding && hasUserName && _authUser == null;
+
+  Future<void> signInWithGoogle() => _auth.signInWithGoogle();
+  Future<void> continueAnonymously() => _auth.signInAnonymously();
 
   ThemeMode _themeMode;
   ThemeMode get themeMode => _themeMode;
@@ -49,6 +74,12 @@ class AppController extends ChangeNotifier {
     notifyListeners();
   }
 
+  @override
+  void dispose() {
+    _authSub.cancel();
+    super.dispose();
+  }
+
   static ThemeMode _decode(String v) => switch (v) {
         'light' => ThemeMode.light,
         'dark' => ThemeMode.dark,

app/lib/ui/core/root_gate.dart

@@ -6,13 +6,14 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
 
+import '../features/onboarding/views/login_screen.dart';
 import '../features/onboarding/views/name_screen.dart';
 import '../features/onboarding/views/onboarding_screen.dart';
 import '../features/onboarding/views/splash_screen.dart';
 import 'app_controller.dart';
 import 'home_shell.dart';
 
-enum _Phase { splash, onboarding, nameEntry, shell }
+enum _Phase { splash, onboarding, nameEntry, login, shell }
 
 class RootGate extends StatefulWidget {
   const RootGate({super.key});
@@ -27,6 +28,7 @@ class _RootGateState extends State<RootGate> {
   _Phase _afterSplash(AppController app) {
     if (!app.seenOnboarding) return _Phase.onboarding;
     if (!app.hasUserName) return _Phase.nameEntry;
+    if (app.needsLogin) return _Phase.login;
     return _Phase.shell;
   }
 
@@ -46,10 +48,18 @@ class _RootGateState extends State<RootGate> {
     await context.read<AppController>().completeOnboarding();
     if (!mounted) return;
     final app = context.read<AppController>();
-    setState(() => _phase = app.hasUserName ? _Phase.shell : _Phase.nameEntry);
+    setState(() => _phase = app.hasUserName
+        ? (app.needsLogin ? _Phase.login : _Phase.shell)
+        : _Phase.nameEntry);
   }
 
   void _finishNameEntry() {
+    if (!mounted) return;
+    final app = context.read<AppController>();
+    setState(() => _phase = app.needsLogin ? _Phase.login : _Phase.shell);
+  }
+
+  void _finishLogin() {
     if (mounted) setState(() => _phase = _Phase.shell);
   }
 
@@ -67,6 +77,8 @@ class _RootGateState extends State<RootGate> {
           OnboardingScreen(key: const ValueKey('onboarding'), onDone: _finishOnboarding),
         _Phase.nameEntry =>
           NameScreen(key: const ValueKey('nameEntry'), onDone: _finishNameEntry),
+        _Phase.login =>
+          LoginScreen(key: const ValueKey('login'), onDone: _finishLogin),
         _Phase.shell => const HomeShell(key: ValueKey('shell')),
       },
     );

app/lib/ui/features/onboarding/views/login_screen.dart

@@ -0,0 +1,134 @@
+/// Login gate, shown after onboarding + name. Google is primary; anonymous is
+/// a quiet escape hatch with an honest data-loss caveat.
+library;
+
+import 'package:flutter/material.dart';
+import 'package:phosphor_flutter/phosphor_flutter.dart';
+import 'package:provider/provider.dart';
+
+import '../../../../data/services/auth_service.dart';
+import '../../../core/brand.dart';
+import '../../../core/widgets/responsive_center.dart';
+
+class LoginScreen extends StatefulWidget {
+  const LoginScreen({super.key, required this.onDone});
+  final VoidCallback onDone;
+
+  @override
+  State<LoginScreen> createState() => _LoginScreenState();
+}
+
+class _LoginScreenState extends State<LoginScreen> {
+  bool _busy = false;
+  String? _error;
+
+  Future<void> _run(Future<void> Function() action) async {
+    setState(() {
+      _busy = true;
+      _error = null;
+    });
+    try {
+      await action();
+      if (mounted) widget.onDone();
+    } catch (_) {
+      if (mounted) {
+        setState(() =>
+            _error = "Couldn't sign in. Check your connection and try again.");
+      }
+    } finally {
+      if (mounted) setState(() => _busy = false);
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final scheme = theme.colorScheme;
+    final auth = context.read<AuthService>();
+    return Scaffold(
+      backgroundColor: scheme.surface,
+      body: Container(
+        decoration: BoxDecoration(
+          gradient: RadialGradient(
+            center: const Alignment(0, -0.45),
+            radius: 1.3,
+            colors: [
+              scheme.primary.withValues(alpha: 0.12),
+              Colors.transparent,
+            ],
+          ),
+        ),
+        child: SafeArea(
+          child: ResponsiveCenter(
+            child: Padding(
+              padding: const EdgeInsets.symmetric(horizontal: 28),
+              child: Column(
+                crossAxisAlignment: CrossAxisAlignment.start,
+                children: [
+                  const SizedBox(height: 48),
+                  const CachyGlyph(size: 56),
+                  const SizedBox(height: 32),
+                  Text('Keep your\nlibrary safe.',
+                      style: theme.textTheme.displaySmall),
+                  const SizedBox(height: 16),
+                  Text(
+                    'Sign in so your cards follow you to any device — and survive a reinstall.',
+                    style: theme.textTheme.bodyLarge?.copyWith(
+                        color: scheme.onSurfaceVariant, height: 1.5),
+                  ),
+                  if (_error != null) ...[
+                    const SizedBox(height: 16),
+                    Text(_error!, style: TextStyle(color: scheme.error)),
+                  ],
+                  const Spacer(),
+                  FilledButton.icon(
+                    onPressed: _busy
+                        ? null
+                        : () => _run(() async {
+                              await auth.signInWithGoogle();
+                            }),
+                    icon: const PhosphorIcon(PhosphorIconsRegular.googleLogo,
+                        size: 20),
+                    label: const Text('Continue with Google'),
+                    style: FilledButton.styleFrom(
+                      minimumSize: const Size.fromHeight(56),
+                      shape: RoundedRectangleBorder(
+                          borderRadius: BorderRadius.circular(16)),
+                    ),
+                  ),
+                  const SizedBox(height: 14),
+                  Center(
+                    child: TextButton(
+                      onPressed: _busy
+                          ? null
+                          : () => _run(() async {
+                                await auth.signInAnonymously();
+                              }),
+                      child: Text(
+                        'Or use without login…',
+                        style: theme.textTheme.bodySmall?.copyWith(
+                          color: scheme.onSurfaceVariant,
+                          decoration: TextDecoration.underline,
+                        ),
+                      ),
+                    ),
+                  ),
+                  const SizedBox(height: 6),
+                  Center(
+                    child: Text(
+                      'Without an account, your library lives only on this device.',
+                      textAlign: TextAlign.center,
+                      style: theme.textTheme.bodySmall
+                          ?.copyWith(color: scheme.onSurfaceVariant),
+                    ),
+                  ),
+                  const SizedBox(height: 24),
+                ],
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}

app/test/auth_service_test.dart

@@ -1,45 +1,6 @@
-import 'dart:async';
-
 import 'package:flutter_test/flutter_test.dart';
-import 'package:cachy/data/services/auth_service.dart';
-
-/// Deterministic in-memory AuthService for widget/unit tests.
-class FakeAuthService implements AuthService {
-  AuthUser? _user;
-  final _controller = StreamController<AuthUser?>.broadcast();
-  String tokenValue = 'fake-token';
-
-  @override
-  Stream<AuthUser?> get userChanges => _controller.stream;
-  @override
-  AuthUser? get currentUser => _user;
-
-  @override
-  Future<AuthUser> signInAnonymously() async {
-    _user = const AuthUser(uid: 'anon-1', isAnonymous: true);
-    _controller.add(_user);
-    return _user!;
-  }
 
-  @override
-  Future<AuthUser> signInWithGoogle() async {
-    // Linking keeps the uid when the current user is anonymous.
-    final uid = _user?.isAnonymous == true ? _user!.uid : 'google-1';
-    _user = AuthUser(uid: uid, isAnonymous: false, email: 'a@b.c', displayName: 'A');
-    _controller.add(_user);
-    return _user!;
-  }
-
-  @override
-  Future<String?> idToken({bool forceRefresh = false}) async =>
-      _user == null ? null : tokenValue;
-
-  @override
-  Future<void> signOut() async {
-    _user = null;
-    _controller.add(null);
-  }
-}
+import 'fakes.dart';
 
 void main() {
   test('google sign-in after anonymous keeps the uid (link semantics)', () async {

app/test/fakes.dart

@@ -0,0 +1,41 @@
+import 'dart:async';
+
+import 'package:cachy/data/services/auth_service.dart';
+
+/// Deterministic in-memory AuthService for widget/unit tests.
+class FakeAuthService implements AuthService {
+  AuthUser? _user;
+  final _controller = StreamController<AuthUser?>.broadcast();
+  String tokenValue = 'fake-token';
+
+  @override
+  Stream<AuthUser?> get userChanges => _controller.stream;
+  @override
+  AuthUser? get currentUser => _user;
+
+  @override
+  Future<AuthUser> signInAnonymously() async {
+    _user = const AuthUser(uid: 'anon-1', isAnonymous: true);
+    _controller.add(_user);
+    return _user!;
+  }
+
+  @override
+  Future<AuthUser> signInWithGoogle() async {
+    // Linking keeps the uid when the current user is anonymous.
+    final uid = _user?.isAnonymous == true ? _user!.uid : 'google-1';
+    _user = AuthUser(uid: uid, isAnonymous: false, email: 'a@b.c', displayName: 'A');
+    _controller.add(_user);
+    return _user!;
+  }
+
+  @override
+  Future<String?> idToken({bool forceRefresh = false}) async =>
+      _user == null ? null : tokenValue;
+
+  @override
+  Future<void> signOut() async {
+    _user = null;
+    _controller.add(null);
+  }
+}

app/test/login_screen_test.dart

@@ -0,0 +1,27 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:provider/provider.dart';
+import 'package:cachy/data/services/auth_service.dart';
+import 'package:cachy/ui/features/onboarding/views/login_screen.dart';
+
+import 'fakes.dart';
+
+void main() {
+  testWidgets('login screen: Google primary, quiet anonymous path', (tester) async {
+    final auth = FakeAuthService();
+    var done = 0;
+    await tester.pumpWidget(
+      Provider<AuthService>.value(
+        value: auth,
+        child: MaterialApp(home: LoginScreen(onDone: () => done++)),
+      ),
+    );
+    expect(find.text('Continue with Google'), findsOneWidget);
+    expect(find.text('Or use without login…'), findsOneWidget);
+
+    await tester.tap(find.text('Or use without login…'));
+    await tester.pumpAndSettle();
+    expect(auth.currentUser?.isAnonymous, isTrue);
+    expect(done, 1);
+  });
+}