fix(auth): an account with a password deletes itself only with it and a code

A session alone deleted any account, with everything encrypted under its
keys (the second reading's lows; decided by the developer: the password
and a code, as a change of password takes). account.delete now takes a
DeletionProof (the password's SRP proof for a beginChange challenge, a
TOTP or recovery code, the host the device addressed); the register
checks it (requireOwnerToDelete), a member passing it on bound to its own
host. Accounts without a password, anonymous ones among them, delete with
their session as before. In the app, deleting an account with a password
asks for it and a code in a sheet of its own; a wrong one deletes
nothing.

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/account_tiles_test.dart

@@ -173,6 +173,54 @@ void main() {
     expect(find.text('Signed out'), findsOneWidget);
   });
 
+  testWidgets('deleting an account with a password asks for it and a '
+      'code, which a wrong one fails, deleting nothing', (tester) async {
+    // The first person the fake password gateway makes.
+    const person = '00000000-0000-4000-8000-000000000001';
+    gateway = FakeAuthGateway(
+      status: const SignedIn(authUserId: person, isIdentified: true),
+    );
+    await start(tester);
+    dependencies.passwordGateway.addAccount(
+      'anna@example.org',
+      password: 'correct horse',
+      crypto: dependencies.crypto,
+    );
+    Finder field(String label) => find.widgetWithText(TextField, label);
+
+    await tester.tap(find.text('Delete account'));
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Delete account').last);
+    await tester.pumpAndSettle();
+
+    expect(gateway.accountDeletions, 0);
+    expect(field('Current password'), findsOneWidget);
+    await tester.enterText(field('Current password'), 'wrong horse');
+    await tester.enterText(
+      field('Code from your authenticator app'),
+      fakeTotpCode,
+    );
+    await tester.tap(find.text('Delete account').last);
+    await tester.pumpAndSettle();
+    expect(
+      find.text("The address, the password or the code isn't right."),
+      findsOneWidget,
+    );
+    expect(gateway.accountDeletions, 0);
+    expect(dependencies.passwordGateway.accounts, contains('anna@example.org'));
+
+    await tester.enterText(field('Current password'), 'correct horse');
+    await tester.tap(find.text('Delete account').last);
+    await tester.pumpAndSettle();
+
+    expect(gateway.accountDeletions, 1);
+    expect(
+      dependencies.passwordGateway.accounts,
+      isNot(contains('anna@example.org')),
+    );
+    expect(find.text('Signed out'), findsOneWidget);
+  });
+
   testWidgets('speaks German', (tester) async {
     await start(tester);
     final german = lookupHalkyonAppLocalizations(const Locale('de'));

packages/halkyon_app/test/password/data/password_repository_test.dart

@@ -302,6 +302,28 @@ void main() {
         expect(anna.password, 'correct horse');
       });
 
+      test('deletes the account with the password and a code alone, then '
+          'signed out here; a wrong one or none deletes nothing', () async {
+        await expectLater(
+          passwords.deleteAccount(password: 'wrong', totpCode: fakeTotpCode),
+          failsWith(PasswordProblem.wrongCredentials),
+        );
+        await expectLater(
+          passwords.deleteAccount(password: 'correct horse'),
+          failsWith(PasswordProblem.wrongCredentials),
+        );
+        expect(gateway.accounts, contains('anna@example.org'));
+        expect(auth.status, isA<SignedIn>());
+
+        await passwords.deleteAccount(
+          password: 'correct horse',
+          totpCode: fakeTotpCode,
+        );
+
+        expect(gateway.accounts, isNot(contains('anna@example.org')));
+        expect(auth.status, const SignedOut());
+      });
+
       test('makes a new recovery phrase, which the instance takes for the '
           'password and a code alone', () async {
         final phrase = await passwords.newPhrase();