halkyon_app: instances, sign-in and sync plumbing for Halkyon's apps

What every Halkyon app's shell needs, taken from Halkyon Learn's and set
on halkyon_base's client: the instances a device keeps an account on,
the first start's tiles and where an instance keeps people's data, the
account switcher; signing in anonymously, with GitHub or an email code,
switching person and the start screen; the gates that build an app's
dependencies per instance and per person; and the sync service with its
status, Settings card and banner. Texts of its own in English and
German take the app's name; what only the app can say, it passes in.
Fakes for apps' tests are in testing.dart.

An instance's basics now name the app it serves (`app`, set by the
host's configuration), and an app accepts only an instance of its own.
SerialQueue and CoalescingRunner move into halkyon_core.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_app/test/auth/widget/session_gate_test.dart

@@ -0,0 +1,173 @@
+import 'package:flutter_bloc/flutter_bloc.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:halkyon_app/halkyon_app.dart';
+import 'package:halkyon_app/testing.dart';
+import 'package:material_ui/material_ui.dart';
+
+/// A signed-in person's app as a test makes one: whose it is, whether
+/// they asked to continue with email, and a way to sign out.
+class const _PersonApp(final SignedIn person) extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) => MaterialApp(
+    localizationsDelegates: testLocalizationsDelegates,
+    supportedLocales: HalkyonAppLocalizations.supportedLocales,
+    home: Scaffold(
+      body: Builder(
+        builder: (context) => Column(
+          children: [
+            Text('App of ${person.authUserId}'),
+            if (context.watch<SessionBloc>().state case SessionStateActive(
+              signsInWithEmail: true,
+            ))
+              const Text('Asks for the address'),
+            TextButton(
+              onPressed: () => context.read<SessionBloc>().add(
+                const SessionEventSignOutRequested(),
+              ),
+              child: const Text('Sign out'),
+            ),
+          ],
+        ),
+      ),
+    ),
+  );
+}
+
+void main() {
+  late FakeAuthGateway gateway;
+  late TestAppDependencies dependencies;
+
+  setUp(() {
+    gateway = FakeAuthGateway();
+    dependencies = TestAppDependencies(gateway: gateway);
+  });
+
+  Future<void> start(WidgetTester tester) async {
+    await tester.pumpWidget(
+      AppFrameScope(
+        frame: testFrame(),
+        child: AppScope(
+          dependencies: dependencies,
+          child: SessionGate(
+            look: (context) => (themeMode: ThemeMode.light, locale: null),
+            app: _PersonApp.new,
+          ),
+        ),
+      ),
+    );
+    await tester.pumpAndSettle();
+  }
+
+  testWidgets('shows the app once signed in anonymously at a first start', (
+    tester,
+  ) async {
+    await start(tester);
+
+    expect(find.text('App of anonymous-1'), findsOneWidget);
+  });
+
+  testWidgets('offers to try again when signing in fails', (tester) async {
+    gateway.signInError = Exception('No connection');
+    await start(tester);
+
+    expect(find.text("Couldn't reach the server."), findsOneWidget);
+
+    gateway.signInError = null;
+    await tester.tap(find.text('Try again'));
+    await tester.pumpAndSettle();
+    expect(find.text('App of anonymous-2'), findsOneWidget);
+  });
+
+  testWidgets('signed out, it asks how to start on the instance, making no '
+      'account; starting without one makes one', (tester) async {
+    await dependencies.signedOut.write(signedOut: true);
+    await start(tester);
+
+    expect(find.text('Signed out'), findsOneWidget);
+    expect(find.text('Start on test.example.org:'), findsOneWidget);
+    expect(find.text('Sign in with GitHub'), findsOneWidget);
+    expect(find.text('Continue with email'), findsOneWidget);
+    expect(
+      find.text('Use another instance'),
+      findsNothing,
+      reason: 'no instances to choose among here',
+    );
+    expect(gateway.signIns, 0);
+
+    await tester.tap(find.text('Start without an account'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('App of anonymous-1'), findsOneWidget);
+    expect(dependencies.signedOut.signedOut, isFalse);
+  });
+
+  testWidgets('from there, GitHub signs in its person; a GitHub account '
+      'nobody here has yet is said so', (tester) async {
+    await dependencies.signedOut.write(signedOut: true);
+    await start(tester);
+
+    gateway.gitHubError = const GitHubSignInFailed(
+      GitHubSignInProblem.unknownAccount,
+    );
+    await tester.tap(find.text('Sign in with GitHub'));
+    await tester.pumpAndSettle();
+    expect(
+      find.text(
+        'No account here signs in with this GitHub account yet. Start '
+        'without an account, then add GitHub in Profile.',
+      ),
+      findsOneWidget,
+    );
+
+    gateway.gitHubError = null;
+    await tester.tap(find.text('Sign in with GitHub'));
+    await tester.pumpAndSettle();
+    expect(find.text('App of github-person'), findsOneWidget);
+    expect(gateway.signIns, 0);
+  });
+
+  testWidgets('from there, an email address starts without an account and '
+      'asks for the address in the app', (tester) async {
+    await dependencies.signedOut.write(signedOut: true);
+    await start(tester);
+
+    await tester.tap(find.text('Continue with email'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('App of anonymous-1'), findsOneWidget);
+    expect(find.text('Asks for the address'), findsOneWidget);
+  });
+
+  testWidgets('offers only the ways the instance has', (tester) async {
+    gateway
+      ..offersGitHub = false
+      ..offersEmail = false;
+    await dependencies.signedOut.write(signedOut: true);
+    await start(tester);
+
+    expect(find.text('Sign in with GitHub'), findsNothing);
+    expect(find.text('Continue with email'), findsNothing);
+    expect(find.text('Start without an account'), findsOneWidget);
+  });
+
+  testWidgets('signing out, or the instance ending the session, asks how to '
+      'start', (tester) async {
+    gateway = FakeAuthGateway(
+      status: const SignedIn(authUserId: 'ada', isIdentified: true),
+    );
+    dependencies = TestAppDependencies(gateway: gateway);
+    await start(tester);
+    expect(find.text('App of ada'), findsOneWidget);
+
+    await tester.tap(find.text('Sign out'));
+    await tester.pumpAndSettle();
+    expect(find.text('Signed out'), findsOneWidget);
+    expect(dependencies.signedOut.signedOut, isTrue);
+
+    await tester.tap(find.text('Start without an account'));
+    await tester.pumpAndSettle();
+    gateway.revokeSession();
+    await tester.pumpAndSettle();
+    expect(find.text('Signed out'), findsOneWidget);
+  });
+}