diff --git a/lib/app/app_controller_desktop_core.dart b/lib/app/app_controller_desktop_core.dart
index 31ec2e02..58827cd2 100644
--- a/lib/app/app_controller_desktop_core.dart
+++ b/lib/app/app_controller_desktop_core.dart
@@ -588,11 +588,7 @@ class AppController extends ChangeNotifier {
       );
 
   List<SingleAgentProvider> get configuredSingleAgentProviders =>
-      normalizeSingleAgentProviderList(
-        bridgeAdvertisedProvidersInternal.where(
-          (item) => item != SingleAgentProvider.auto,
-        ),
-      );
+      normalizeSingleAgentProviderList(bridgeAdvertisedProvidersInternal);
 
   List<SingleAgentProvider> get availableSingleAgentProviders =>
       availableSingleAgentProvidersOverrideInternal != null
@@ -638,11 +634,10 @@ class AppController extends ChangeNotifier {
   bool canUseSingleAgentProviderInternal(SingleAgentProvider provider) {
     final override = availableSingleAgentProvidersOverrideInternal;
     if (override != null) {
-      return provider != SingleAgentProvider.auto &&
-          override.contains(provider);
+      return !provider.isUnspecified && override.contains(provider);
     }
-    if (provider == SingleAgentProvider.auto) {
-      return hasAnyAvailableSingleAgentProvider;
+    if (provider.isUnspecified) {
+      return false;
     }
     final capabilities = singleAgentCapabilitiesByProviderInternal[provider];
     return capabilities?.available == true &&
@@ -652,7 +647,7 @@ class AppController extends ChangeNotifier {
   SingleAgentProvider? resolvedSingleAgentProviderInternal(
     SingleAgentProvider selection,
   ) {
-    if (selection == SingleAgentProvider.auto) {
+    if (selection.isUnspecified) {
       return null;
     }
     return canUseSingleAgentProviderInternal(selection) ? selection : null;
diff --git a/lib/app/app_controller_desktop_runtime_helpers.dart b/lib/app/app_controller_desktop_runtime_helpers.dart
index c3c0e33e..21a1c96b 100644
--- a/lib/app/app_controller_desktop_runtime_helpers.dart
+++ b/lib/app/app_controller_desktop_runtime_helpers.dart
@@ -235,7 +235,7 @@ extension AppControllerDesktopRuntimeHelpers on AppController {
         );
         final provider =
             resolvedSingleAgentProviderInternal(selection) ?? selection;
-        final providerLabel = provider == SingleAgentProvider.auto
+        final providerLabel = provider.isUnspecified
             ? appText('Bridge Provider', 'Bridge Provider')
             : provider.label;
         final address = _extractGatewayAddressFromErrorInternal(raw);
diff --git a/lib/app/app_controller_desktop_settings.dart b/lib/app/app_controller_desktop_settings.dart
index 912f7cf7..92118e80 100644
--- a/lib/app/app_controller_desktop_settings.dart
+++ b/lib/app/app_controller_desktop_settings.dart
@@ -311,7 +311,7 @@ extension AppControllerDesktopSettings on AppController {
         currentSettings.assistantExecutionTarget,
       ),
       messageViewMode: AssistantMessageViewMode.rendered,
-      singleAgentProvider: SingleAgentProvider.auto,
+      singleAgentProvider: SingleAgentProvider.unspecified,
     );
     await setCurrentAssistantSessionKeyInternal(
       'main',
diff --git a/lib/app/app_controller_desktop_single_agent_go_task_flow.dart b/lib/app/app_controller_desktop_single_agent_go_task_flow.dart
index 369717cd..929b54af 100644
--- a/lib/app/app_controller_desktop_single_agent_go_task_flow.dart
+++ b/lib/app/app_controller_desktop_single_agent_go_task_flow.dart
@@ -98,7 +98,7 @@ Future<void> sendSingleAgentMessageDesktopGoTaskFlowInternal(
                   effectiveProvider == null)
           ? (routingResolution.unavailableMessage.isNotEmpty
                 ? routingResolution.unavailableMessage
-                : selection == SingleAgentProvider.auto
+                : selection.isUnspecified
                 ? appText(
                     '当前没有可用的 GoTaskService Provider。',
                     'No GoTaskService provider is currently available.',
@@ -177,7 +177,7 @@ Future<void> sendSingleAgentMessageDesktopGoTaskFlowInternal(
             routingResolution,
           ),
           routingHint: 'single-agent',
-          provider: effectiveProvider ?? SingleAgentProvider.auto,
+          provider: effectiveProvider ?? SingleAgentProvider.unspecified,
           remoteWorkingDirectoryHint:
               controller
                   .requireTaskThreadForSessionInternal(sessionKey)
diff --git a/lib/app/app_controller_desktop_skill_permissions.dart b/lib/app/app_controller_desktop_skill_permissions.dart
index 9672ff15..9b183c6a 100644
--- a/lib/app/app_controller_desktop_skill_permissions.dart
+++ b/lib/app/app_controller_desktop_skill_permissions.dart
@@ -306,7 +306,7 @@ extension AppControllerDesktopSkillPermissions on AppController {
                 executionBinding?.providerId ??
                     existing?.executionBinding.providerId,
               ))
-        : SingleAgentProvider.auto;
+        : SingleAgentProvider.unspecified;
     final nextProviderSource =
         nextExecutionTarget == AssistantExecutionTarget.singleAgent
         ? (singleAgentProviderSource ??
diff --git a/lib/app/app_controller_desktop_thread_binding.dart b/lib/app/app_controller_desktop_thread_binding.dart
index 671852c4..156b02eb 100644
--- a/lib/app/app_controller_desktop_thread_binding.dart
+++ b/lib/app/app_controller_desktop_thread_binding.dart
@@ -258,7 +258,7 @@ extension AppControllerDesktopThreadBinding on AppController {
     final sanitizedProvider =
         executionTarget == AssistantExecutionTarget.singleAgent
         ? settings.sanitizeSingleAgentProviderSelection(singleAgentProvider)
-        : SingleAgentProvider.auto;
+        : SingleAgentProvider.unspecified;
     return (existingBinding ??
             ExecutionBinding(
               executionMode: ThreadExecutionMode.localAgent,
diff --git a/lib/app/app_controller_desktop_thread_sessions.dart b/lib/app/app_controller_desktop_thread_sessions.dart
index 659d8899..54c8461b 100644
--- a/lib/app/app_controller_desktop_thread_sessions.dart
+++ b/lib/app/app_controller_desktop_thread_sessions.dart
@@ -254,7 +254,12 @@ extension AppControllerDesktopThreadSessions on AppController {
           )?.executionBinding.providerId ??
           '',
     );
-    return settings.sanitizeSingleAgentProviderSelection(stored);
+    final sanitized = settings.sanitizeSingleAgentProviderSelection(stored);
+    if (!sanitized.isUnspecified) {
+      return sanitized;
+    }
+    final options = singleAgentProviderOptions;
+    return options.isEmpty ? SingleAgentProvider.unspecified : options.first;
   }
 
   SingleAgentProvider get currentSingleAgentProvider =>
@@ -304,7 +309,7 @@ extension AppControllerDesktopThreadSessions on AppController {
       return false;
     }
     final selection = singleAgentProviderForSession(normalizedSessionKey);
-    if (selection == SingleAgentProvider.auto) {
+    if (selection.isUnspecified) {
       return false;
     }
     return !canUseSingleAgentProviderInternal(selection) &&
@@ -385,7 +390,7 @@ extension AppControllerDesktopThreadSessions on AppController {
       return resolvedProvider.label;
     }
     final provider = currentSingleAgentProvider;
-    if (provider != SingleAgentProvider.auto) {
+    if (!provider.isUnspecified) {
       return provider.label;
     }
     return appText('单机智能体', 'Single Agent');
diff --git a/lib/app/app_controller_desktop_thread_storage.dart b/lib/app/app_controller_desktop_thread_storage.dart
index 0b1e3035..db2575a8 100644
--- a/lib/app/app_controller_desktop_thread_storage.dart
+++ b/lib/app/app_controller_desktop_thread_storage.dart
@@ -693,7 +693,7 @@ extension AppControllerDesktopThreadStorage on AppController {
                 record.executionBinding.providerId,
               ),
             )
-          : SingleAgentProvider.auto;
+          : SingleAgentProvider.unspecified;
       final workspaceBinding = record.workspaceBinding.copyWith(
         workspaceId: sessionKey,
         displayPath: record.workspaceKind == WorkspaceKind.localFs
diff --git a/lib/app/app_controller_desktop_workspace_execution.dart b/lib/app/app_controller_desktop_workspace_execution.dart
index 06ba4ddd..c86efa47 100644
--- a/lib/app/app_controller_desktop_workspace_execution.dart
+++ b/lib/app/app_controller_desktop_workspace_execution.dart
@@ -361,7 +361,7 @@ extension AppControllerDesktopWorkspaceExecution on AppController {
       singleAgentProvider:
           singleAgentProvider ??
           singleAgentProviderForSession(currentSessionKey),
-      singleAgentProviderSource: ThreadSelectionSource.explicit,
+      singleAgentProviderSource: ThreadSelectionSource.inherited,
       updatedAtMs: DateTime.now().millisecondsSinceEpoch.toDouble(),
     );
     // Re-read the current thread target when the async binding sync runs so a
diff --git a/lib/features/assistant/assistant_page_composer_support.dart b/lib/features/assistant/assistant_page_composer_support.dart
index 89db6c89..7b727538 100644
--- a/lib/features/assistant/assistant_page_composer_support.dart
+++ b/lib/features/assistant/assistant_page_composer_support.dart
@@ -219,24 +219,19 @@ class SingleAgentProviderBadgeInternal extends StatelessWidget {
     final candidate = provider.badge.trim().isEmpty
         ? provider.label
         : provider.badge;
-    final display = candidate.length <= 2
+    final display = candidate.trim().isEmpty
+        ? '?'
+        : candidate.length <= 2
         ? candidate
         : candidate.substring(0, 2);
-    final isAuto = provider == SingleAgentProvider.auto;
     return Container(
       width: 18,
       height: 18,
       alignment: Alignment.center,
       decoration: BoxDecoration(
-        color: isAuto
-            ? palette.accent.withValues(alpha: 0.16)
-            : palette.surfaceSecondary,
+        color: palette.surfaceSecondary,
         borderRadius: BorderRadius.circular(999),
-        border: Border.all(
-          color: isAuto
-              ? palette.accent.withValues(alpha: 0.4)
-              : palette.strokeSoft,
-        ),
+        border: Border.all(color: palette.strokeSoft),
       ),
       child: Text(
         display,
diff --git a/lib/features/assistant/assistant_page_tooltip_labels.dart b/lib/features/assistant/assistant_page_tooltip_labels.dart
index 4c300d60..d2649475 100644
--- a/lib/features/assistant/assistant_page_tooltip_labels.dart
+++ b/lib/features/assistant/assistant_page_tooltip_labels.dart
@@ -43,11 +43,12 @@ String executionTargetTooltipInternal(AssistantExecutionTarget target) =>
       'Task dialog mode: ${target.compactLabel}',
     );
 
-String singleAgentProviderTooltipInternal(SingleAgentProvider provider) =>
-    appText(
-      'Bridge Provider: ${provider.label}',
-      'Bridge Provider: ${provider.label}',
-    );
+String singleAgentProviderTooltipInternal(
+  SingleAgentProvider provider,
+) => appText(
+  'Bridge Provider: ${provider.label.trim().isEmpty ? appText('未配置', 'Unconfigured') : provider.label}',
+  'Bridge Provider: ${provider.label.trim().isEmpty ? appText('未配置', 'Unconfigured') : provider.label}',
+);
 
 String modelTooltipInternal(String modelLabel) =>
     appText('模型: $modelLabel', 'Model: $modelLabel');
diff --git a/lib/runtime/external_code_agent_acp_desktop_transport.dart b/lib/runtime/external_code_agent_acp_desktop_transport.dart
index 5c746c82..0f13fed5 100644
--- a/lib/runtime/external_code_agent_acp_desktop_transport.dart
+++ b/lib/runtime/external_code_agent_acp_desktop_transport.dart
@@ -201,7 +201,7 @@ class ExternalCodeAgentAcpDesktopTransport
         providerId,
         label: label?.isNotEmpty == true ? label : null,
       );
-      if (provider != SingleAgentProvider.auto) {
+      if (!provider.isUnspecified) {
         providers.add(provider);
       }
     }
diff --git a/lib/runtime/gateway_acp_client.dart b/lib/runtime/gateway_acp_client.dart
index d7792c1c..881f6da4 100644
--- a/lib/runtime/gateway_acp_client.dart
+++ b/lib/runtime/gateway_acp_client.dart
@@ -158,7 +158,7 @@ class GatewayAcpClient {
         providerId,
         label: label?.isNotEmpty == true ? label : null,
       );
-      if (provider != SingleAgentProvider.auto) {
+      if (!provider.isUnspecified) {
         providers.add(provider);
       }
     }
diff --git a/lib/runtime/go_task_service_client.dart b/lib/runtime/go_task_service_client.dart
index a6cc23de..2210c6bb 100644
--- a/lib/runtime/go_task_service_client.dart
+++ b/lib/runtime/go_task_service_client.dart
@@ -219,7 +219,7 @@ class GoTaskServiceRequest {
     required this.metadata,
     this.routing,
     this.routingHint = '',
-    this.provider = SingleAgentProvider.auto,
+    this.provider = SingleAgentProvider.unspecified,
     this.remoteWorkingDirectoryHint = '',
     this.resumeSession = false,
     this.collaborationMode = GoTaskServiceCollaborationMode.standard,
@@ -322,7 +322,7 @@ class GoTaskServiceRequest {
               },
             )
             .toList(growable: false),
-      if (provider != SingleAgentProvider.auto) 'provider': provider.providerId,
+      if (!provider.isUnspecified) 'provider': provider.providerId,
       if (remoteWorkingDirectoryHint.trim().isNotEmpty)
         'remoteWorkingDirectoryHint': remoteWorkingDirectoryHint.trim(),
       if (model.trim().isNotEmpty) 'model': model.trim(),
@@ -353,7 +353,7 @@ class GoTaskServiceRequest {
       AssistantExecutionTarget.remote => 'remote',
       AssistantExecutionTarget.singleAgent => 'singleAgent',
     };
-    final explicitProviderId = provider == SingleAgentProvider.auto
+    final explicitProviderId = provider.isUnspecified
         ? ''
         : provider.providerId;
     final explicitModelValue = model.trim();
diff --git a/lib/runtime/runtime_models_connection.dart b/lib/runtime/runtime_models_connection.dart
index f63321aa..e7cc58ac 100644
--- a/lib/runtime/runtime_models_connection.dart
+++ b/lib/runtime/runtime_models_connection.dart
@@ -167,7 +167,7 @@ String normalizeSingleAgentProviderId(String value) {
 String singleAgentProviderFallbackLabelInternal(String providerId) {
   final normalized = normalizeSingleAgentProviderId(providerId);
   if (normalized.isEmpty) {
-    return 'Custom Agent';
+    return appText('Bridge Provider', 'Bridge Provider');
   }
   return normalized
       .split(RegExp(r'[-_.]+'))
@@ -182,7 +182,6 @@ String singleAgentProviderFallbackBadgeInternal({
 }) {
   final normalized = normalizeSingleAgentProviderId(providerId);
   final known = <String, String>{
-    'auto': 'A',
     'codex': 'C',
     'opencode': 'O',
     'claude': 'Cl',
@@ -225,10 +224,10 @@ class SingleAgentProvider {
     this.source = SingleAgentProviderSource.externalExtension,
   });
 
-  static const SingleAgentProvider auto = SingleAgentProvider(
-    providerId: 'auto',
-    label: 'Auto',
-    badge: 'A',
+  static const SingleAgentProvider unspecified = SingleAgentProvider(
+    providerId: '',
+    label: '',
+    badge: '',
   );
 
   static const SingleAgentProvider codex = SingleAgentProvider(
@@ -260,7 +259,7 @@ class SingleAgentProvider {
   final String badge;
   final SingleAgentProviderSource source;
 
-  bool get isAuto => providerId == auto.providerId;
+  bool get isUnspecified => providerId.trim().isEmpty;
   bool get isExternalExtension =>
       source == SingleAgentProviderSource.externalExtension;
 
@@ -301,7 +300,7 @@ class SingleAgentProvider {
       'opencode' => opencode,
       'claude' => claude,
       'gemini' => gemini,
-      'auto' || '' => auto,
+      'auto' || '' => unspecified,
       _ => SingleAgentProvider(
         providerId: normalized,
         label: singleAgentProviderFallbackLabelInternal(normalized),
diff --git a/lib/runtime/runtime_models_profiles.dart b/lib/runtime/runtime_models_profiles.dart
index a526565f..a45e7726 100644
--- a/lib/runtime/runtime_models_profiles.dart
+++ b/lib/runtime/runtime_models_profiles.dart
@@ -100,7 +100,7 @@ class ExternalAcpEndpointProfile {
       json['providerKey']?.toString() ?? '',
     );
     final builtin = SingleAgentProviderCopy.fromJsonValue(providerKey);
-    final fallbackLabel = builtin.isAuto ? providerKey : builtin.label;
+    final fallbackLabel = builtin.isUnspecified ? providerKey : builtin.label;
     final label = json['label']?.toString().trim().isNotEmpty == true
         ? json['label'].toString().trim()
         : fallbackLabel;
@@ -132,9 +132,6 @@ List<ExternalAcpEndpointProfile> normalizeExternalAcpEndpoints({
   ) {
     final key = profile.providerKey.trim().toLowerCase();
     for (final provider in kKnownSingleAgentProviders) {
-      if (provider.isAuto) {
-        continue;
-      }
       if (provider.providerId == key) {
         return provider;
       }
@@ -142,9 +139,6 @@ List<ExternalAcpEndpointProfile> normalizeExternalAcpEndpoints({
     final label = profile.label.trim();
     final badge = profile.badge.trim();
     for (final provider in kKnownSingleAgentProviders) {
-      if (provider.isAuto) {
-        continue;
-      }
       if (provider.label == label && provider.badge == badge) {
         return provider;
       }
diff --git a/lib/runtime/runtime_models_runtime_payloads.dart b/lib/runtime/runtime_models_runtime_payloads.dart
index b79dc69a..6dc56fa5 100644
--- a/lib/runtime/runtime_models_runtime_payloads.dart
+++ b/lib/runtime/runtime_models_runtime_payloads.dart
@@ -1019,8 +1019,8 @@ class TaskThread {
            executionBinding ??
            ExecutionBinding(
              executionMode: ThreadExecutionMode.localAgent,
-             executorId: SingleAgentProvider.auto.providerId,
-             providerId: SingleAgentProvider.auto.providerId,
+             executorId: SingleAgentProvider.unspecified.providerId,
+             providerId: SingleAgentProvider.unspecified.providerId,
              endpointId: '',
            ),
        contextState =
diff --git a/lib/runtime/runtime_models_settings_snapshot.dart b/lib/runtime/runtime_models_settings_snapshot.dart
index 952da557..42e5839c 100644
--- a/lib/runtime/runtime_models_settings_snapshot.dart
+++ b/lib/runtime/runtime_models_settings_snapshot.dart
@@ -447,8 +447,8 @@ class SettingsSnapshot {
   }
 
   SingleAgentProvider resolveSingleAgentProvider(SingleAgentProvider provider) {
-    if (provider.isAuto) {
-      return SingleAgentProvider.auto;
+    if (provider.isUnspecified) {
+      return SingleAgentProvider.unspecified;
     }
     final profile = providerSyncDefinitionForProviderId(provider.providerId);
     if (profile != null) {
@@ -459,8 +459,8 @@ class SettingsSnapshot {
 
   SingleAgentProvider singleAgentProviderForId(String providerId) {
     final resolved = normalizeSingleAgentProviderId(providerId);
-    if (resolved.isEmpty || resolved == SingleAgentProvider.auto.providerId) {
-      return SingleAgentProvider.auto;
+    if (resolved.isEmpty || resolved == 'auto') {
+      return SingleAgentProvider.unspecified;
     }
     final normalizedSelection = SingleAgentProvider.fromJsonValue(resolved);
     final profile = providerSyncDefinitionForProviderId(
@@ -476,8 +476,8 @@ class SettingsSnapshot {
     SingleAgentProvider provider,
   ) {
     final resolved = resolveSingleAgentProvider(provider);
-    if (resolved.isAuto) {
-      return SingleAgentProvider.auto;
+    if (resolved.isUnspecified) {
+      return SingleAgentProvider.unspecified;
     }
     if (kKnownSingleAgentProviders.any(
       (item) => item.providerId == resolved.providerId,
diff --git a/test/app_controller_desktop_runtime_cleanup_test.dart b/test/app_controller_desktop_runtime_cleanup_test.dart
index b5a18544..b61525e7 100644
--- a/test/app_controller_desktop_runtime_cleanup_test.dart
+++ b/test/app_controller_desktop_runtime_cleanup_test.dart
@@ -175,6 +175,63 @@ void main() {
       );
     },
   );
+
+  test(
+    'single-agent threads default to bridge catalog providers without reviving auto mode',
+    () async {
+      final root = Directory.systemTemp.createTempSync(
+        'xworkmate-provider-selection-test-',
+      );
+      final store = SecureConfigStore(
+        enableSecureStorage: false,
+        appDataRootPathResolver: () async => root.path,
+        secretRootPathResolver: () async => root.path,
+        supportRootPathResolver: () async => root.path,
+      );
+      final controller = AppController(
+        store: store,
+        desktopPlatformService: UnsupportedDesktopPlatformService(),
+        skillDirectoryAccessService: _FakeSkillDirectoryAccessService(
+          root.path,
+        ),
+        goTaskServiceClient: const _FakeGoTaskServiceClient(),
+        singleAgentSharedSkillScanRootOverrides: const <String>[],
+        availableSingleAgentProvidersOverride: const <SingleAgentProvider>[
+          SingleAgentProvider.codex,
+        ],
+      );
+      addTearDown(() async {
+        controller.dispose();
+        if (root.existsSync()) {
+          await root.delete(recursive: true);
+        }
+      });
+
+      expect(
+        controller.singleAgentProviderForSession('draft:bridge-default'),
+        SingleAgentProvider.codex,
+      );
+
+      controller.initializeAssistantThreadContext(
+        'draft:bridge-default',
+        executionTarget: AssistantExecutionTarget.singleAgent,
+      );
+
+      final thread = controller.taskThreadForSessionInternal(
+        'draft:bridge-default',
+      );
+      expect(thread, isNotNull);
+      expect(
+        thread!.executionBinding.providerId,
+        SingleAgentProvider.codex.providerId,
+      );
+      expect(
+        thread.executionBinding.providerSource,
+        ThreadSelectionSource.inherited,
+      );
+      expect(thread.hasExplicitProviderSelection, isFalse);
+    },
+  );
 }
 
 class _FakeSkillDirectoryAccessService implements SkillDirectoryAccessService {
diff --git a/test/app_controller_desktop_thread_binding_test.dart b/test/app_controller_desktop_thread_binding_test.dart
index 09191f12..99ce5892 100644
--- a/test/app_controller_desktop_thread_binding_test.dart
+++ b/test/app_controller_desktop_thread_binding_test.dart
@@ -102,7 +102,7 @@ void main() {
       );
 
       expect(snapshot.executionTarget, AssistantExecutionTarget.remote);
-      expect(snapshot.singleAgentProvider, SingleAgentProvider.auto);
+      expect(snapshot.singleAgentProvider.isUnspecified, isTrue);
       expect(snapshot.record, isNull);
       expect(staleRecord.executionBinding.providerId, isNotEmpty);
     });
diff --git a/test/app_controller_desktop_thread_target_cleanup_test.dart b/test/app_controller_desktop_thread_target_cleanup_test.dart
index 4482aefd..bdcfe8f3 100644
--- a/test/app_controller_desktop_thread_target_cleanup_test.dart
+++ b/test/app_controller_desktop_thread_target_cleanup_test.dart
@@ -14,7 +14,7 @@ void main() {
     TaskThread buildThread({
       required String threadId,
       required ThreadExecutionMode mode,
-      String providerId = 'auto',
+      String providerId = '',
     }) {
       return TaskThread(
         threadId: threadId,