blocked all nextcloud requests in demo mode to stop fake-credential logins tripping brute-force protection

lib/api/demo/demo_http_client.dart

@@ -0,0 +1,28 @@
+import 'package:http/http.dart' as http;
+import 'package:http/io_client.dart';
+
+import '../../model/endpoint_data.dart';
+import '../errors/network_exception.dart';
+import 'demo_mode.dart';
+
+/// Demo sessions carry made-up credentials. Every request they sent to the
+/// real Nextcloud would count as a failed login there and, in bulk, trip the
+/// server's brute-force throttle for the whole IP (HTTP 429 for everyone
+/// behind it). Installed app-wide via [http.runWithClient].
+class DemoHttpClient extends http.BaseClient {
+  final http.Client _inner = IOClient();
+
+  @override
+  Future<http.StreamedResponse> send(http.BaseRequest request) {
+    if (DemoMode.active && isNextcloudHost(request.url)) {
+      return Future.error(NetworkException.demoBlocked(request.url));
+    }
+    return _inner.send(request);
+  }
+
+  @override
+  void close() => _inner.close();
+
+  static bool isNextcloudHost(Uri url) =>
+      url.host == EndpointData().nextcloud().domain;
+}