add draft changes

lib/services/navigation_guard.dart

@@ -0,0 +1,40 @@
+typedef NavigationGuardCallback = Future<bool> Function();
+
+class NavigationGuard {
+  static NavigationGuardCallback? _callback;
+
+  static void register(NavigationGuardCallback callback) {
+    _callback = callback;
+  }
+
+  static void unregister(NavigationGuardCallback callback) {
+    if (_callback == callback) {
+      _callback = null;
+    }
+  }
+
+  static Future<void> attemptNavigation(
+    Future<void> Function() performNavigation,
+  ) async {
+    if (_promptActive) return;
+    final cb = _callback;
+    if (cb == null) {
+      await performNavigation();
+      return;
+    }
+    _promptActive = true;
+    bool allow = false;
+    try {
+      allow = await cb();
+    } catch (_) {
+      allow = false;
+    } finally {
+      _promptActive = false;
+    }
+    if (allow) {
+      await performNavigation();
+    }
+  }
+
+  static bool _promptActive = false;
+}