diff --git a/lib/app/app_controller_desktop.dart b/lib/app/app_controller_desktop.dart
index 6e164432..384611bc 100644
--- a/lib/app/app_controller_desktop.dart
+++ b/lib/app/app_controller_desktop.dart
@@ -205,6 +205,8 @@ class AppController extends ChangeNotifier {
       <String, List<GatewayChatMessage>>{};
   final Map<String, String> _aiGatewayStreamingTextBySession =
       <String, String>{};
+  final Map<String, String> _singleAgentRuntimeModelBySession =
+      <String, String>{};
   final Map<String, HttpClient> _aiGatewayStreamingClients =
       <String, HttpClient>{};
   final Set<String> _aiGatewayPendingSessionKeys = <String>{};
@@ -517,6 +519,19 @@ class AppController extends ChangeNotifier {
   String assistantModelForSession(String sessionKey) {
     final normalizedSessionKey = _normalizedAssistantSessionKey(sessionKey);
     final target = assistantExecutionTargetForSession(normalizedSessionKey);
+    if (target == AssistantExecutionTarget.singleAgent) {
+      if (singleAgentUsesAiChatFallbackForSession(normalizedSessionKey)) {
+        final recordModel =
+            _assistantThreadRecords[normalizedSessionKey]?.assistantModelId
+                .trim() ??
+            '';
+        if (recordModel.isNotEmpty) {
+          return recordModel;
+        }
+        return resolvedAiGatewayModel;
+      }
+      return singleAgentRuntimeModelForSession(normalizedSessionKey);
+    }
     final recordModel =
         _assistantThreadRecords[normalizedSessionKey]?.assistantModelId
             .trim() ??
@@ -524,10 +539,6 @@ class AppController extends ChangeNotifier {
     if (recordModel.isNotEmpty) {
       return recordModel;
     }
-    if (target == AssistantExecutionTarget.singleAgent &&
-        singleAgentUsesAiChatFallbackForSession(normalizedSessionKey)) {
-      return resolvedAiGatewayModel;
-    }
     return _resolvedAssistantModelForTarget(target);
   }
 
@@ -603,8 +614,20 @@ class AppController extends ChangeNotifier {
   bool get currentSingleAgentShouldSuggestAutoSwitch =>
       singleAgentShouldSuggestAutoSwitchForSession(currentSessionKey);
 
+  String singleAgentRuntimeModelForSession(String sessionKey) {
+    final normalizedSessionKey = _normalizedAssistantSessionKey(sessionKey);
+    return _singleAgentRuntimeModelBySession[normalizedSessionKey]?.trim() ?? '';
+  }
+
+  String get currentSingleAgentRuntimeModel =>
+      singleAgentRuntimeModelForSession(currentSessionKey);
+
   String singleAgentModelDisplayLabelForSession(String sessionKey) {
     final normalizedSessionKey = _normalizedAssistantSessionKey(sessionKey);
+    final runtimeModel = singleAgentRuntimeModelForSession(normalizedSessionKey);
+    if (runtimeModel.isNotEmpty) {
+      return runtimeModel;
+    }
     final model = assistantModelForSession(normalizedSessionKey);
     if (model.isNotEmpty) {
       return model;
@@ -624,6 +647,21 @@ class AppController extends ChangeNotifier {
   String get currentSingleAgentModelDisplayLabel =>
       singleAgentModelDisplayLabelForSession(currentSessionKey);
 
+  bool singleAgentShouldShowModelControlForSession(String sessionKey) {
+    final normalizedSessionKey = _normalizedAssistantSessionKey(sessionKey);
+    if (assistantExecutionTargetForSession(normalizedSessionKey) !=
+        AssistantExecutionTarget.singleAgent) {
+      return true;
+    }
+    if (singleAgentUsesAiChatFallbackForSession(normalizedSessionKey)) {
+      return true;
+    }
+    return singleAgentRuntimeModelForSession(normalizedSessionKey).isNotEmpty;
+  }
+
+  bool get currentSingleAgentShouldShowModelControl =>
+      singleAgentShouldShowModelControlForSession(currentSessionKey);
+
   List<SingleAgentProvider> get singleAgentProviderOptions =>
       const <SingleAgentProvider>[
         SingleAgentProvider.auto,
@@ -1786,6 +1824,7 @@ class AppController extends ChangeNotifier {
     if (singleAgentProviderForSession(sessionKey) == sanitizedProvider) {
       return;
     }
+    _singleAgentRuntimeModelBySession.remove(sessionKey);
     _upsertAssistantThreadRecord(
       sessionKey,
       singleAgentProvider: sanitizedProvider,
@@ -1838,6 +1877,9 @@ class AppController extends ChangeNotifier {
   }) async {
     final resolvedTarget = _sanitizeExecutionTarget(target);
     final normalizedSessionKey = _normalizedAssistantSessionKey(sessionKey);
+    if (resolvedTarget != AssistantExecutionTarget.singleAgent) {
+      _singleAgentRuntimeModelBySession.remove(normalizedSessionKey);
+    }
     if (!matchesSessionKey(
       normalizedSessionKey,
       _sessionsController.currentSessionKey,
@@ -3209,6 +3251,10 @@ class AppController extends ChangeNotifier {
             configuredCodexCliPath: configuredCodexCliPath,
           ),
         );
+        final resolvedRuntimeModel = result.resolvedModel.trim();
+        if (resolvedRuntimeModel.isNotEmpty) {
+          _singleAgentRuntimeModelBySession[sessionKey] = resolvedRuntimeModel;
+        }
         _clearAiGatewayStreamingText(sessionKey);
         if (result.aborted) {
           final partial = result.output.trim();
diff --git a/lib/features/assistant/assistant_page.dart b/lib/features/assistant/assistant_page.dart
index 2c9a9141..1bdb895c 100644
--- a/lib/features/assistant/assistant_page.dart
+++ b/lib/features/assistant/assistant_page.dart
@@ -459,6 +459,9 @@ class _AssistantPageState extends State<AssistantPage> {
                 inputController: _inputController,
                 focusNode: _composerFocusNode,
                 thinkingLabel: _thinkingLabel,
+                showModelControl: !controller.isSingleAgentMode
+                    ? true
+                    : controller.currentSingleAgentShouldShowModelControl,
                 modelLabel: controller.isSingleAgentMode
                     ? controller.currentSingleAgentModelDisplayLabel
                     : controller.resolvedAssistantModel.isEmpty
@@ -1617,6 +1620,7 @@ class _AssistantLowerPane extends StatelessWidget {
     required this.inputController,
     required this.focusNode,
     required this.thinkingLabel,
+    required this.showModelControl,
     required this.modelLabel,
     required this.modelOptions,
     required this.attachments,
@@ -1638,6 +1642,7 @@ class _AssistantLowerPane extends StatelessWidget {
   final TextEditingController inputController;
   final FocusNode focusNode;
   final String thinkingLabel;
+  final bool showModelControl;
   final String modelLabel;
   final List<String> modelOptions;
   final List<_ComposerAttachment> attachments;
@@ -1665,6 +1670,7 @@ class _AssistantLowerPane extends StatelessWidget {
           inputController: inputController,
           focusNode: focusNode,
           thinkingLabel: thinkingLabel,
+          showModelControl: showModelControl,
           modelLabel: modelLabel,
           modelOptions: modelOptions,
           attachments: attachments,
@@ -2495,6 +2501,7 @@ class _ComposerBar extends StatefulWidget {
     required this.inputController,
     required this.focusNode,
     required this.thinkingLabel,
+    required this.showModelControl,
     required this.modelLabel,
     required this.modelOptions,
     required this.attachments,
@@ -2516,6 +2523,7 @@ class _ComposerBar extends StatefulWidget {
   final TextEditingController inputController;
   final FocusNode focusNode;
   final String thinkingLabel;
+  final bool showModelControl;
   final String modelLabel;
   final List<String> modelOptions;
   final List<_ComposerAttachment> attachments;
@@ -2899,43 +2907,45 @@ class _ComposerBarState extends State<_ComposerBar> {
                           maxLabelWidth: 120,
                         ),
                       ),
-                      const SizedBox(width: 6),
-                      widget.modelOptions.isEmpty
-                          ? _ComposerToolbarChip(
-                              key: const Key('assistant-model-button'),
-                              icon: Icons.bolt_rounded,
-                              label: widget.modelLabel,
-                              showChevron: false,
-                              maxLabelWidth: 140,
-                            )
-                          : PopupMenuButton<String>(
-                              key: const Key('assistant-model-button'),
-                              tooltip: appText('模型', 'Model'),
-                              onSelected: widget.onModelChanged,
-                              itemBuilder: (context) => widget.modelOptions
-                                  .map(
-                                    (value) => PopupMenuItem<String>(
-                                      value: value,
-                                      child: Row(
-                                        children: [
-                                          Expanded(child: Text(value)),
-                                          if (value == widget.modelLabel)
-                                            const Icon(
-                                              Icons.check_rounded,
-                                              size: 18,
-                                            ),
-                                        ],
-                                      ),
-                                    ),
-                                  )
-                                  .toList(),
-                              child: _ComposerToolbarChip(
+                      if (widget.showModelControl) ...[
+                        const SizedBox(width: 6),
+                        widget.modelOptions.isEmpty
+                            ? _ComposerToolbarChip(
+                                key: const Key('assistant-model-button'),
                                 icon: Icons.bolt_rounded,
                                 label: widget.modelLabel,
-                                showChevron: true,
+                                showChevron: false,
                                 maxLabelWidth: 140,
+                              )
+                            : PopupMenuButton<String>(
+                                key: const Key('assistant-model-button'),
+                                tooltip: appText('模型', 'Model'),
+                                onSelected: widget.onModelChanged,
+                                itemBuilder: (context) => widget.modelOptions
+                                    .map(
+                                      (value) => PopupMenuItem<String>(
+                                        value: value,
+                                        child: Row(
+                                          children: [
+                                            Expanded(child: Text(value)),
+                                            if (value == widget.modelLabel)
+                                              const Icon(
+                                                Icons.check_rounded,
+                                                size: 18,
+                                              ),
+                                          ],
+                                        ),
+                                      ),
+                                    )
+                                    .toList(),
+                                child: _ComposerToolbarChip(
+                                  icon: Icons.bolt_rounded,
+                                  label: widget.modelLabel,
+                                  showChevron: true,
+                                  maxLabelWidth: 140,
+                                ),
                               ),
-                            ),
+                      ],
                       const SizedBox(width: 6),
                       PopupMenuButton<String>(
                         key: const Key('assistant-thinking-button'),
diff --git a/lib/runtime/direct_single_agent_app_server_client.dart b/lib/runtime/direct_single_agent_app_server_client.dart
index e83799aa..2c1fbc6a 100644
--- a/lib/runtime/direct_single_agent_app_server_client.dart
+++ b/lib/runtime/direct_single_agent_app_server_client.dart
@@ -35,12 +35,14 @@ class DirectSingleAgentRunResult {
     required this.output,
     required this.errorMessage,
     this.aborted = false,
+    this.resolvedModel = '',
   });
 
   final bool success;
   final String output;
   final String errorMessage;
   final bool aborted;
+  final String resolvedModel;
 }
 
 class DirectSingleAgentRunRequest {
@@ -166,6 +168,7 @@ class DirectSingleAgentAppServerClient {
       );
 
       final output = StringBuffer();
+      String resolvedModel = '';
       final completion = Completer<DirectSingleAgentRunResult>();
       late final StreamSubscription<Map<String, dynamic>> subscription;
       subscription = connection.notifications.listen(
@@ -189,6 +192,7 @@ class DirectSingleAgentAppServerClient {
                 success: true,
                 output: output.toString(),
                 errorMessage: '',
+                resolvedModel: resolvedModel,
               ),
             );
             return;
@@ -206,6 +210,7 @@ class DirectSingleAgentAppServerClient {
                 success: false,
                 output: output.toString(),
                 aborted: aborted,
+                resolvedModel: resolvedModel,
                 errorMessage:
                     params['message']?.toString() ??
                     params['error']?.toString() ??
@@ -222,6 +227,7 @@ class DirectSingleAgentAppServerClient {
                 output: output.toString(),
                 errorMessage: error.toString(),
                 aborted: _abortedSessions.contains(normalizedSessionId),
+                resolvedModel: resolvedModel,
               ),
             );
           }
@@ -236,6 +242,7 @@ class DirectSingleAgentAppServerClient {
                     ? 'Single-agent app-server run aborted.'
                     : 'Single-agent app-server connection closed before completion.',
                 aborted: _abortedSessions.contains(normalizedSessionId),
+                resolvedModel: resolvedModel,
               ),
             );
           }
@@ -243,7 +250,7 @@ class DirectSingleAgentAppServerClient {
       );
 
       try {
-        await connection.request(
+        final started = await connection.request(
           'turn/start',
           params: <String, dynamic>{
             'threadId': threadId,
@@ -253,6 +260,7 @@ class DirectSingleAgentAppServerClient {
             },
           },
         );
+        resolvedModel = _extractModel(started) ?? resolvedModel;
         return await completion.future.timeout(
           const Duration(minutes: 10),
           onTimeout: () => DirectSingleAgentRunResult(
@@ -260,6 +268,7 @@ class DirectSingleAgentAppServerClient {
             output: output.toString(),
             errorMessage: 'Single-agent app-server request timed out.',
             aborted: _abortedSessions.contains(normalizedSessionId),
+            resolvedModel: resolvedModel,
           ),
         );
       } finally {
@@ -271,6 +280,7 @@ class DirectSingleAgentAppServerClient {
         output: '',
         errorMessage: error.toString(),
         aborted: _abortedSessions.contains(normalizedSessionId),
+        resolvedModel: '',
       );
     } finally {
       _activeConnections.remove(normalizedSessionId);
@@ -325,7 +335,7 @@ class DirectSingleAgentAppServerClient {
             if (workingDirectory.trim().isNotEmpty) 'cwd': workingDirectory,
           },
         );
-        final resumedId = resumed['id']?.toString().trim() ?? existingThreadId;
+        final resumedId = _extractThreadId(resumed) ?? existingThreadId;
         _threadIds[sessionId] = resumedId;
         return resumedId;
       } catch (_) {
@@ -340,7 +350,7 @@ class DirectSingleAgentAppServerClient {
         if (model.trim().isNotEmpty) 'model': model.trim(),
       },
     );
-    final threadId = created['id']?.toString().trim() ?? '';
+    final threadId = _extractThreadId(created) ?? '';
     if (threadId.isEmpty) {
       throw StateError('Single-agent app-server returned an empty thread id.');
     }
@@ -348,6 +358,27 @@ class DirectSingleAgentAppServerClient {
     return threadId;
   }
 
+  String? _extractThreadId(Map<String, dynamic> payload) {
+    final topLevelId = payload['id']?.toString().trim() ?? '';
+    if (topLevelId.isNotEmpty) {
+      return topLevelId;
+    }
+    final thread = _asMap(payload['thread']);
+    final nestedId = thread['id']?.toString().trim() ?? '';
+    if (nestedId.isNotEmpty) {
+      return nestedId;
+    }
+    return null;
+  }
+
+  String? _extractModel(Map<String, dynamic> payload) {
+    final model = payload['model']?.toString().trim() ?? '';
+    if (model.isNotEmpty) {
+      return model;
+    }
+    return null;
+  }
+
   Uri? _resolveWebSocketEndpoint(SingleAgentProvider provider) {
     final base = endpointResolver(provider);
     if (base == null) {
diff --git a/lib/runtime/single_agent_runner.dart b/lib/runtime/single_agent_runner.dart
index ef914a98..0bf528a7 100644
--- a/lib/runtime/single_agent_runner.dart
+++ b/lib/runtime/single_agent_runner.dart
@@ -55,6 +55,7 @@ class SingleAgentRunResult {
     required this.shouldFallbackToAiChat,
     this.aborted = false,
     this.fallbackReason,
+    this.resolvedModel = '',
   });
 
   final SingleAgentProvider provider;
@@ -64,6 +65,7 @@ class SingleAgentRunResult {
   final bool shouldFallbackToAiChat;
   final bool aborted;
   final String? fallbackReason;
+  final String resolvedModel;
 }
 
 abstract class SingleAgentRunner {
@@ -166,6 +168,7 @@ class DefaultSingleAgentRunner implements SingleAgentRunner {
         errorMessage: result.errorMessage,
         shouldFallbackToAiChat: !result.success && result.output.isEmpty,
         aborted: result.aborted,
+        resolvedModel: result.resolvedModel,
         fallbackReason: !result.success
             ? 'Single-agent app-server run failed: ${result.errorMessage}'
             : null,
@@ -178,6 +181,7 @@ class DefaultSingleAgentRunner implements SingleAgentRunner {
         success: false,
         errorMessage: error.toString(),
         shouldFallbackToAiChat: shouldFallback,
+        resolvedModel: '',
         fallbackReason: shouldFallback
             ? '${request.provider.label} provider is unavailable from the direct app-server endpoint.'
             : null,
diff --git a/test/runtime/app_controller_ai_gateway_chat_suite.dart b/test/runtime/app_controller_ai_gateway_chat_suite.dart
index 2b1bd486..a73a4906 100644
--- a/test/runtime/app_controller_ai_gateway_chat_suite.dart
+++ b/test/runtime/app_controller_ai_gateway_chat_suite.dart
@@ -349,6 +349,7 @@ void main() {
           success: true,
           errorMessage: '',
           shouldFallbackToAiChat: false,
+          resolvedModel: 'codex-sonnet',
         ),
       );
       final controller = AppController(
@@ -375,6 +376,8 @@ void main() {
       expect(runner.resolveCalls, 1);
       expect(runner.runCalls, 1);
       expect(runner.lastRequest?.provider, SingleAgentProvider.codex);
+      expect(runner.lastRequest?.model, isEmpty);
+      expect(controller.currentSingleAgentModelDisplayLabel, 'codex-sonnet');
       expect(
         controller.chatMessages.any(
           (message) =>
diff --git a/test/runtime/app_controller_ai_gateway_models_suite.dart b/test/runtime/app_controller_ai_gateway_models_suite.dart
index 88c62e56..67b2f0a7 100644
--- a/test/runtime/app_controller_ai_gateway_models_suite.dart
+++ b/test/runtime/app_controller_ai_gateway_models_suite.dart
@@ -136,6 +136,7 @@ void main() {
 
       expect(controller.currentSingleAgentHasResolvedProvider, isTrue);
       expect(controller.currentSingleAgentUsesAiChatFallback, isFalse);
+      expect(controller.currentSingleAgentShouldShowModelControl, isFalse);
       expect(controller.assistantModelChoices, isEmpty);
       expect(controller.resolvedAssistantModel, isEmpty);
     },
diff --git a/test/runtime/direct_single_agent_app_server_suite.dart b/test/runtime/direct_single_agent_app_server_suite.dart
index 06bfa5f8..f451b181 100644
--- a/test/runtime/direct_single_agent_app_server_suite.dart
+++ b/test/runtime/direct_single_agent_app_server_suite.dart
@@ -52,6 +52,7 @@ void main() {
 
       expect(result.success, isTrue);
       expect(result.output, 'hello world from app server');
+      expect(result.resolvedModel, 'codex-sonnet');
       expect(deltas.join(), 'hello world from app server');
       expect(
         server.methods,
@@ -87,14 +88,47 @@ void main() {
       expect(result.aborted, isTrue);
       expect(server.methods, contains('turn/interrupt'));
     });
+
+    test(
+      'accepts nested thread objects returned by codex app-server',
+      () async {
+        final server = await _FakeAppServer.start(nestedThreadResult: true);
+        addTearDown(server.close);
+
+        final client = DirectSingleAgentAppServerClient(
+          endpointResolver: (_) => server.baseHttpUri,
+        );
+        addTearDown(client.dispose);
+
+        final result = await client.run(
+          const DirectSingleAgentRunRequest(
+            sessionId: 'session-nested',
+            provider: SingleAgentProvider.codex,
+            prompt: 'hello nested world',
+            model: 'qwen2.5-coder:latest',
+            workingDirectory: '/tmp',
+            gatewayToken: '',
+          ),
+        );
+
+        expect(result.success, isTrue);
+        expect(result.output, 'hello world from app server');
+        expect(result.resolvedModel, 'codex-sonnet');
+      },
+    );
   });
 }
 
 class _FakeAppServer {
-  _FakeAppServer._(this._server, {required this.delayCompletion});
+  _FakeAppServer._(
+    this._server, {
+    required this.delayCompletion,
+    required this.nestedThreadResult,
+  });
 
   final HttpServer _server;
   final bool delayCompletion;
+  final bool nestedThreadResult;
   final List<String> methods = <String>[];
   final List<String> authorizationHeaders = <String>[];
   final Map<String, Completer<void>> _methodWaiters =
@@ -104,9 +138,16 @@ class _FakeAppServer {
   int get port => _server.port;
   Uri get baseHttpUri => Uri.parse('http://127.0.0.1:${_server.port}');
 
-  static Future<_FakeAppServer> start({bool delayCompletion = false}) async {
+  static Future<_FakeAppServer> start({
+    bool delayCompletion = false,
+    bool nestedThreadResult = false,
+  }) async {
     final server = await HttpServer.bind(InternetAddress.loopbackIPv4, 0);
-    final fake = _FakeAppServer._(server, delayCompletion: delayCompletion);
+    final fake = _FakeAppServer._(
+      server,
+      delayCompletion: delayCompletion,
+      nestedThreadResult: nestedThreadResult,
+    );
     unawaited(fake._listen());
     return fake;
   }
@@ -166,28 +207,46 @@ class _FakeAppServer {
           break;
         case 'thread/start':
           _threadCounter += 1;
+          final result = nestedThreadResult
+              ? <String, dynamic>{
+                  'thread': <String, dynamic>{
+                    'id': 'thread-$_threadCounter',
+                    'path': params['cwd'] ?? '/tmp',
+                    'ephemeral': false,
+                  },
+                }
+              : <String, dynamic>{
+                  'id': 'thread-$_threadCounter',
+                  'path': params['cwd'] ?? '/tmp',
+                  'ephemeral': false,
+                };
           socket.add(
             jsonEncode(<String, dynamic>{
               'jsonrpc': '2.0',
               'id': id,
-              'result': <String, dynamic>{
-                'id': 'thread-$_threadCounter',
-                'path': params['cwd'] ?? '/tmp',
-                'ephemeral': false,
-              },
+              'result': result,
             }),
           );
           break;
         case 'thread/resume':
+          final result = nestedThreadResult
+              ? <String, dynamic>{
+                  'thread': <String, dynamic>{
+                    'id': params['threadId'] ?? 'thread-resumed',
+                    'path': params['cwd'] ?? '/tmp',
+                    'ephemeral': false,
+                  },
+                }
+              : <String, dynamic>{
+                  'id': params['threadId'] ?? 'thread-resumed',
+                  'path': params['cwd'] ?? '/tmp',
+                  'ephemeral': false,
+                };
           socket.add(
             jsonEncode(<String, dynamic>{
               'jsonrpc': '2.0',
               'id': id,
-              'result': <String, dynamic>{
-                'id': params['threadId'] ?? 'thread-resumed',
-                'path': params['cwd'] ?? '/tmp',
-                'ephemeral': false,
-              },
+              'result': result,
             }),
           );
           break;
@@ -201,6 +260,7 @@ class _FakeAppServer {
                 'id': 'turn-1',
                 'threadId': threadId,
                 'status': 'started',
+                'model': 'codex-sonnet',
               },
             }),
           );