Fix chat.send metadata regression across gateway clients

lib/runtime/gateway_runtime_api.dart

@@ -146,7 +146,6 @@ extension GatewayRuntimeApiInternal on GatewayRuntime {
           'idempotencyKey': runId,
           if (agentId != null && agentId.trim().isNotEmpty)
             'agentId': agentId.trim(),
-          if (metadata != null && metadata.isNotEmpty) 'metadata': metadata,
           if (attachments.isNotEmpty)
             'attachments': attachments
                 .map((attachment) => attachment.toJson())

lib/web/web_relay_gateway_client.dart

@@ -294,10 +294,6 @@ class WebRelayGatewayClient {
     Map<String, dynamic> metadata = const <String, dynamic>{},
   }) async {
     final runId = randomIdInternal();
-    final normalizedMetadata = <String, dynamic>{
-      for (final entry in metadata.entries)
-        if (entry.key.trim().isNotEmpty) entry.key: entry.value,
-    };
     final payload = asMapInternal(
       await request(
         'chat.send',
@@ -309,7 +305,6 @@ class WebRelayGatewayClient {
             'attachments': attachments
                 .map((item) => item.toJson())
                 .toList(growable: false),
-          if (normalizedMetadata.isNotEmpty) 'metadata': normalizedMetadata,
           'timeoutMs': 30000,
           'idempotencyKey': runId,
         },

test/runtime/gateway_runtime_suite.dart

@@ -34,6 +34,24 @@ void main() {
     );
   });
 
+  test('GatewayRuntime omits metadata from chat.send payloads', () async {
+    SharedPreferences.setMockInitialValues(<String, Object>{});
+    final store = createIsolatedTestStore();
+    final runtime = _FakeGatewayRuntimeForSendChat(store: store);
+
+    final runId = await runtime.sendChat(
+      sessionKey: 'thread-1',
+      message: 'hello',
+      thinking: 'medium',
+      metadata: const <String, dynamic>{'threadMode': 'test'},
+    );
+
+    expect(runId, 'run-send-chat');
+    expect(runtime.lastMethod, 'chat.send');
+    expect(runtime.lastParams, isNotNull);
+    expect(runtime.lastParams, isNot(contains('metadata')));
+  });
+
   test(
     'GatewayRuntime uses explicit shared token override for the initial connect handshake',
     () async {
@@ -669,6 +687,25 @@ class _FakeGatewayRuntimeForChatController extends GatewayRuntime {
   }
 }
 
+class _FakeGatewayRuntimeForSendChat extends GatewayRuntime {
+  _FakeGatewayRuntimeForSendChat({required super.store})
+    : super(identityStore: DeviceIdentityStore(store));
+
+  String? lastMethod;
+  Map<String, dynamic>? lastParams;
+
+  @override
+  Future<dynamic> request(
+    String method, {
+    Map<String, dynamic>? params,
+    Duration timeout = const Duration(seconds: 15),
+  }) async {
+    lastMethod = method;
+    lastParams = params == null ? null : Map<String, dynamic>.from(params);
+    return const <String, dynamic>{'runId': 'run-send-chat'};
+  }
+}
+
 class FakeGatewayRuntimeServerInternal {
   FakeGatewayRuntimeServerInternal._(
     this.serverInternal, {

test/web/web_relay_gateway_client_test.dart

@@ -0,0 +1,49 @@
+@TestOn('vm')
+library;
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+import 'package:xworkmate/runtime/runtime_models.dart';
+import 'package:xworkmate/web/web_relay_gateway_client.dart';
+import 'package:xworkmate/web/web_store.dart';
+
+class _FakeWebRelayGatewayClient extends WebRelayGatewayClient {
+  _FakeWebRelayGatewayClient() : super(WebStore());
+
+  String? lastMethod;
+  Map<String, dynamic>? lastParams;
+
+  @override
+  bool get isConnected => true;
+
+  @override
+  Future<dynamic> request(
+    String method, {
+    Map<String, dynamic>? params,
+    Duration timeout = const Duration(seconds: 15),
+  }) async {
+    lastMethod = method;
+    lastParams = params == null ? null : Map<String, dynamic>.from(params);
+    return const <String, dynamic>{'runId': 'relay-run'};
+  }
+}
+
+void main() {
+  test('WebRelayGatewayClient omits metadata from chat.send payloads', () async {
+    SharedPreferences.setMockInitialValues(<String, Object>{});
+    final client = _FakeWebRelayGatewayClient();
+
+    final runId = await client.sendChat(
+      sessionKey: 'thread-1',
+      message: 'hello',
+      thinking: 'medium',
+      metadata: const <String, dynamic>{'threadMode': 'test'},
+      attachments: const <GatewayChatAttachmentPayload>[],
+    );
+
+    expect(runId, 'relay-run');
+    expect(client.lastMethod, 'chat.send');
+    expect(client.lastParams, isNotNull);
+    expect(client.lastParams, isNot(contains('metadata')));
+  });
+}