Check for pending invitations before creating new Family during SSO log in/sign up (#1171)

* Check for pending invitations before creating new Family during SSO account creation

When a user signs in via Google SSO and doesn't have an account yet, the
system now checks for pending invitations before creating a new Family.
If an invitation exists, the user joins the invited family instead.

- OidcAccountsController: check Invitation.pending in link/create_user
- API AuthController: check pending invitations in sso_create_account
- SessionsController: pass has_pending_invitation to mobile SSO callback
- Web view: show "Accept Invitation" button when invitation exists
- Flutter: show "Accept Invitation" tab/button when invitation pending

https://claude.ai/code/session_019Tr6edJa496V1ErGmsbqFU

* Fix external assistant tests: clear Settings cache to prevent test pollution

The tests relied solely on with_env_overrides to clear configuration, but
rails-settings-cached may retain stale Setting values across tests when
the cache isn't explicitly invalidated. Ensure both ENV vars AND Setting
values are cleared with Setting.clear_cache before assertions.

https://claude.ai/code/session_019Tr6edJa496V1ErGmsbqFU

---------

Co-authored-by: Claude <noreply@anthropic.com>

mobile/lib/providers/auth_provider.dart

@@ -29,6 +29,7 @@ class AuthProvider with ChangeNotifier {
   String? _ssoFirstName;
   String? _ssoLastName;
   bool _ssoAllowAccountCreation = false;
+  bool _ssoHasPendingInvitation = false;
 
   User? get user => _user;
   bool get isIntroLayout => _user?.isIntroLayout ?? false;
@@ -51,6 +52,7 @@ class AuthProvider with ChangeNotifier {
   String? get ssoFirstName => _ssoFirstName;
   String? get ssoLastName => _ssoLastName;
   bool get ssoAllowAccountCreation => _ssoAllowAccountCreation;
+  bool get ssoHasPendingInvitation => _ssoHasPendingInvitation;
 
   AuthProvider() {
     _loadStoredAuth();
@@ -294,6 +296,7 @@ class AuthProvider with ChangeNotifier {
         _ssoFirstName = result['first_name'] as String?;
         _ssoLastName = result['last_name'] as String?;
         _ssoAllowAccountCreation = result['allow_account_creation'] == true;
+        _ssoHasPendingInvitation = result['has_pending_invitation'] == true;
         _isLoading = false;
         notifyListeners();
         return false;
@@ -410,6 +413,7 @@ class AuthProvider with ChangeNotifier {
     _ssoFirstName = null;
     _ssoLastName = null;
     _ssoAllowAccountCreation = false;
+    _ssoHasPendingInvitation = false;
   }
 
   Future<void> logout() async {

mobile/lib/screens/sso_onboarding_screen.dart

@@ -148,7 +148,9 @@ class _SsoOnboardingScreenState extends State<SsoOnboardingScreen> {
                           ),
                           Expanded(
                             child: _TabButton(
-                              label: 'Create New',
+                              label: authProvider.ssoHasPendingInvitation
+                                  ? 'Accept Invitation'
+                                  : 'Create New',
                               isSelected: !_showLinkForm,
                               onTap: () =>
                                   setState(() => _showLinkForm = false),
@@ -258,6 +260,7 @@ class _SsoOnboardingScreenState extends State<SsoOnboardingScreen> {
   }
 
   Widget _buildCreateForm(AuthProvider authProvider, ColorScheme colorScheme) {
+    final hasPendingInvitation = authProvider.ssoHasPendingInvitation;
     return Form(
       key: _createFormKey,
       child: Column(
@@ -271,11 +274,16 @@ class _SsoOnboardingScreenState extends State<SsoOnboardingScreen> {
             ),
             child: Row(
               children: [
-                Icon(Icons.person_add, color: colorScheme.primary),
+                Icon(
+                  hasPendingInvitation ? Icons.mail_outline : Icons.person_add,
+                  color: colorScheme.primary,
+                ),
                 const SizedBox(width: 12),
                 Expanded(
                   child: Text(
-                    'Create a new account using your Google identity.',
+                    hasPendingInvitation
+                        ? 'You have a pending invitation. Accept it to join an existing household.'
+                        : 'Create a new account using your Google identity.',
                     style: TextStyle(color: colorScheme.onSurface),
                   ),
                 ),
@@ -318,7 +326,9 @@ class _SsoOnboardingScreenState extends State<SsoOnboardingScreen> {
                     width: 20,
                     child: CircularProgressIndicator(strokeWidth: 2),
                   )
-                : const Text('Create Account'),
+                : Text(hasPendingInvitation
+                        ? 'Accept Invitation'
+                        : 'Create Account'),
           ),
         ],
       ),

mobile/lib/services/auth_service.dart

@@ -374,6 +374,7 @@ class AuthService {
         'first_name': params['first_name'] ?? '',
         'last_name': params['last_name'] ?? '',
         'allow_account_creation': params['allow_account_creation'] == 'true',
+        'has_pending_invitation': params['has_pending_invitation'] == 'true',
       };
     }