fixed guardian login edge cases and misleading placeholders on failed loads

test/view/parent_letters/parent_letter_form_policy_test.dart

@@ -75,13 +75,22 @@ void main() {
       expect(policy.mode, ParentLetterFormMode.done);
     });
 
-    test('unknown optional fields are skipped', () {
+    test('unknown optional fields are skipped but flagged', () {
       final policy = ParentLetterFormPolicy.resolve(
         request: const ParentLetterRequest(fields: [_choice, _unknownOptional]),
         child: _child(),
       )!;
       expect(policy.mode, ParentLetterFormMode.open);
       expect(policy.fields, [_choice]);
+      expect(policy.hasUnsupportedFields, isTrue);
+    });
+
+    test('a fully supported request is not flagged', () {
+      final policy = ParentLetterFormPolicy.resolve(
+        request: const ParentLetterRequest(fields: [_choice, _optionalChoice]),
+        child: _child(),
+      )!;
+      expect(policy.hasUnsupportedFields, isFalse);
     });
   });