feat(app): adding SimpleLogin to an account (ADR 0020, D21, D23)

halkyon_app reads where the device's person stands with SimpleLogin
(nothing to show, linked, or missing) and shows it in SimpleLoginSection,
which each app places above the password part: Add SimpleLogin, once
added one more way in. GitHub is added to nobody where SimpleLogin is
offered, and Learn's Profile offers an anonymous person SimpleLogin
alone there (D23).

No cut-off day, reminder or banner (D24): with the developer the only
person on learn.halkyon.eu, the cut-off is the operator taking GitHub's
OAuth app out of the deploy's settings once that account has SimpleLogin.
ADR 0020 records it and drops step 5.

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/simplelogin/widget/simplelogin_section_test.dart

@@ -0,0 +1,117 @@
+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';
+
+const password = 'correct horse battery';
+
+void main() {
+  late FakeAuthGateway gateway;
+  late TestAppDependencies dependencies;
+
+  setUp(() {
+    gateway = FakeAuthGateway();
+    dependencies = TestAppDependencies(gateway: gateway);
+    dependencies.simpleLoginGateway.isOffered = true;
+  });
+  tearDown(() => dependencies.dispose());
+
+  /// An app's account section.
+  Future<void> show(WidgetTester tester) async {
+    tester.view.physicalSize = const Size(412, 1200);
+    tester.view.devicePixelRatio = 1;
+    addTearDown(tester.view.reset);
+    await tester.pumpWidget(
+      testApp(
+        const Scaffold(
+          body: Padding(
+            padding: EdgeInsets.symmetric(horizontal: 16),
+            child: SimpleLoginSection(gapAbove: 16),
+          ),
+        ),
+        dependencies: dependencies,
+      ),
+    );
+    await tester.pumpAndSettle();
+  }
+
+  Future<void> signInAccount() =>
+      gateway.useSession(const SessionGrant('person-9', 'session-9'));
+
+  testWidgets('an account without SimpleLogin is offered to add it', (
+    tester,
+  ) async {
+    await signInAccount();
+    await show(tester);
+
+    expect(find.text('SimpleLogin'), findsOneWidget);
+    expect(find.widgetWithText(ListTile, 'Add SimpleLogin'), findsOneWidget);
+    expect(
+      find.text('Sign in with SimpleLogin, or with your Proton account.'),
+      findsOneWidget,
+    );
+  });
+
+  testWidgets('nothing where the instance offers no SimpleLogin', (
+    tester,
+  ) async {
+    dependencies.simpleLoginGateway.isOffered = false;
+    await signInAccount();
+    await show(tester);
+
+    expect(find.textContaining('SimpleLogin'), findsNothing);
+  });
+
+  testWidgets('an account that has it: one more way in', (tester) async {
+    dependencies.simpleLoginGateway.addAccount(
+      'person-9',
+      subject: 'simplelogin-ben',
+    );
+    await signInAccount();
+    await show(tester);
+
+    expect(find.widgetWithText(ListTile, 'SimpleLogin'), findsOneWidget);
+    expect(find.text('Signs you in'), findsOneWidget);
+    expect(find.text('Add SimpleLogin'), findsNothing);
+  });
+
+  testWidgets('adding it: an account with its keys is done once the browser '
+      'is back, says so, and shows it as a way in', (tester) async {
+    final material = await dependencies.crypto.newKeys(password);
+    dependencies.simpleLoginGateway.accounts['person-9'] =
+        FakeSimpleLoginAccount(handle: 'ben', keys: material.setup);
+    await signInAccount();
+    await show(tester);
+
+    await tester.tap(find.widgetWithText(ListTile, 'Add SimpleLogin'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('SimpleLogin added.'), findsOneWidget);
+    expect(dependencies.simpleLoginGateway.linked, {
+      'simplelogin-anna': 'person-9',
+    });
+    expect(find.text('Signs you in'), findsOneWidget);
+  });
+
+  testWidgets("a SimpleLogin account that is another account's is refused", (
+    tester,
+  ) async {
+    dependencies.simpleLoginGateway.addAccount(
+      'person-7',
+      subject: 'simplelogin-anna',
+    );
+    await signInAccount();
+    await show(tester);
+
+    await tester.tap(find.widgetWithText(ListTile, 'Add SimpleLogin'));
+    await tester.pumpAndSettle();
+
+    expect(
+      find.text('This SimpleLogin account belongs to another account here.'),
+      findsOneWidget,
+    );
+    expect(dependencies.simpleLoginGateway.linked, {
+      'simplelogin-anna': 'person-7',
+    });
+  });
+}