fix navbar freezing fix

lib/services/data_service/data_service_core.dart

@@ -209,22 +209,46 @@ class DataService extends ChangeNotifier {
     final target = date ?? DateTime.now();
     final formatted =
         "${target.year.toString().padLeft(4, '0')}-${target.month.toString().padLeft(2, '0')}-${target.day.toString().padLeft(2, '0')}";
+    final endpoint = '/legs/on-this-day?date=$formatted';
+    dynamic json;
+    Object? lastError;
+    for (int attempt = 0; attempt < 2; attempt++) {
+      try {
+        json = await api.get(endpoint);
+        lastError = null;
+        break;
+      } catch (e) {
+        lastError = e;
+        if (!_looksLikeOnThisDayRoutingConflict(e)) break;
+        await Future<void>.delayed(const Duration(milliseconds: 250));
+      }
+    }
+
     try {
-      final json = await api.get('/legs/on-this-day?date=$formatted');
       if (json is List) {
         _onThisDay = json.map((e) => Leg.fromJson(e)).toList();
       } else {
         _onThisDay = [];
       }
     } catch (e) {
-      debugPrint('Failed to fetch on-this-day legs: $e');
+      lastError ??= e;
       _onThisDay = [];
     } finally {
+      if (lastError != null) {
+        debugPrint('Failed to fetch on-this-day legs ($endpoint): $lastError');
+      }
       _isOnThisDayLoading = false;
       _notifyAsync();
     }
   }
 
+  bool _looksLikeOnThisDayRoutingConflict(Object error) {
+    final msg = error.toString();
+    return msg.contains('API error 422') &&
+        msg.contains('[path, loco_id]') &&
+        msg.contains('input: on-this-day');
+  }
+
   Future<void> fetchEventFields({bool force = false}) async {
     if (_eventFields.isNotEmpty && !force) return;
     _isEventFieldsLoading = true;

lib/services/navigation_guard.dart

@@ -7,9 +7,10 @@ class NavigationGuard {
     _callback = callback;
   }
 
-  static void unregister(NavigationGuardCallback callback) {
-    if (_callback == callback) {
+  static void unregister([NavigationGuardCallback? callback]) {
+    if (callback == null || identical(_callback, callback)) {
       _callback = null;
+      _promptActive = false;
     }
   }