TF-4404 Keep automation keys stable across enum renames.

integration_test/scenarios/calendar/mail_to_attendees_event_email_scenario.dart

@@ -17,6 +17,8 @@ class MailToAttendeesEventEmailScenario extends BaseTestScenario
     with OpenCalendarEventScenarioMixin {
   const MailToAttendeesEventEmailScenario(super.$);
 
+  static const _expectedEventTitle = 'Come for a chat';
+
   @override
   Future<void> runTestLogic() async {
     final threadRobot = ThreadRobot($);
@@ -51,7 +53,7 @@ class MailToAttendeesEventEmailScenario extends BaseTestScenario
     final actualSubject = composerController.subjectEmail.value ?? '';
 
     final expectedSubject = EmailUtils.applyPrefix(
-      subject: 'Come for a chat',
+      subject: _expectedEventTitle,
       defaultPrefix: EmailUtils.defaultReplyPrefix,
       localizedPrefix: appLocalizations.prefix_reply_email,
     );

lib/features/email/domain/model/event_action.dart

@@ -24,7 +24,20 @@ enum EventActionType {
     }
   }
 
-  Key getKeyButton() => Key('${name}_event_action_button');
+  Key getKeyButton() {
+    switch (this) {
+      case EventActionType.yes:
+        return const Key('yes_event_action_button');
+      case EventActionType.acceptCounter:
+        return const Key('acceptCounter_event_action_button');
+      case EventActionType.maybe:
+        return const Key('maybe_event_action_button');
+      case EventActionType.no:
+        return const Key('no_event_action_button');
+      case EventActionType.mailToAttendees:
+        return const Key('mailToAttendees_event_action_button');
+    }
+  }
 
   String getToastMessageSuccess(BuildContext context) {
     switch(this) {

test/features/email/presentation/apply_prefix_test.dart

@@ -184,6 +184,19 @@ void main() {
           equals('  Re: Hello'),
         );
       });
+
+      test(
+        'should add a standardized prefix for a legacy NBSP variant',
+        () {
+          expect(
+            EmailUtils.applyPrefix(
+              subject: 'Re\u00A0: Hello',
+              defaultPrefix: EmailUtils.defaultReplyPrefix,
+            ),
+            equals('Re: Re\u00A0: Hello'),
+          );
+        },
+      );
     });
   });
 }