feat(mcp): friendly UI message when stdio MCP refused by Box state

Previously the MCP detail dialog dumped the raw RuntimeError text from
``_init_stdio_python_server`` — English-only, prefixed with "Failed
after 4 attempts", and exposing internal config names. The retry
wrapper also kept retrying a refusal that is deterministically going
to fail again, polluting logs.

Replace the raw text with a structured signal:

- New ``MCPSessionErrorPhase.BOX_UNAVAILABLE`` enum value. The stdio
  refusal path sets it before raising and uses a short opaque
  discriminator (``box_disabled_in_config`` / ``box_unavailable``) as
  the message body — never user-facing
- ``_lifecycle_loop_with_retry`` short-circuits on
  ``BOX_UNAVAILABLE``: surfaces the error immediately, no retries,
  no "Failed after N attempts" prefix. Silences the warning storm
  seen during smoke-testing
- ``MCPServerRuntimeInfo`` (TS type) now declares ``error_phase``,
  ``retry_count``, ``box_session_id``, ``box_enabled`` to match what
  the backend already returns in get_runtime_info_dict()
- Both MCP detail forms (``mcp/components/mcp-form/MCPForm.tsx`` and
  ``plugins/mcp-server/mcp-form/MCPFormDialog.tsx``) detect
  ``error_phase === 'box_unavailable'`` and render a two-line
  localized notice: state line ("Box disabled / unreachable") plus
  remediation line ("enable Box or switch to http/sse")
- 8 locale files (en/zh-Hans/zh-Hant/ja/ru/vi/th/es) get
  ``mcp.boxDisabledStdioRefused``, ``mcp.boxUnavailableStdioRefused``,
  ``mcp.boxStdioRefusedSuggestion``

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/langbot/pkg/provider/tools/loaders/mcp.py

@@ -94,19 +94,18 @@ class RuntimeMCPSession:
         # (disabled by config or connection failed). Refuse stdio MCP rather
         # than silently falling through to host-stdio — the operator asked
         # for the sandbox and the failure mode should be visible.
+        #
+        # Set ``error_phase = BOX_UNAVAILABLE`` BEFORE raising so the retry
+        # wrapper can short-circuit (retrying is pointless when Box is
+        # deliberately off) and the frontend can render a localized,
+        # actionable message instead of this raw RuntimeError. Keep the
+        # message itself short — the frontend ignores it for this phase.
         box_service = getattr(self.ap, 'box_service', None)
         if box_service is not None and not getattr(box_service, 'available', False):
-            connector_error = getattr(box_service, '_connector_error', '') or 'currently unavailable'
+            self.error_phase = MCPSessionErrorPhase.BOX_UNAVAILABLE
             if not getattr(box_service, 'enabled', True):
-                reason = 'disabled in config (box.enabled = false)'
-            else:
-                reason = f'unavailable: {connector_error}'
-            raise RuntimeError(
-                f'Stdio MCP server "{self.server_name}" requires the Box runtime, '
-                f'which is {reason}. Either enable Box in config.yaml '
-                f'(box.enabled = true) and ensure the runtime is healthy, '
-                f'or switch this MCP server to http/sse transport.'
-            )
+                raise RuntimeError('box_disabled_in_config')
+            raise RuntimeError('box_unavailable')
 
         # Legacy: no box_service installed at all (pre-Box dev mode). Fall
         # through to host-stdio for backward compatibility.
@@ -231,6 +230,14 @@ class RuntimeMCPSession:
                 self.retry_count = attempt + 1
                 if self._shutdown_event.is_set():
                     return  # Shutdown requested, don't retry
+                # BOX_UNAVAILABLE is a deliberate refusal, not a transient
+                # failure — retrying produces log spam and a misleading
+                # "Failed after N attempts" message. Surface it immediately.
+                if self.error_phase == MCPSessionErrorPhase.BOX_UNAVAILABLE:
+                    self.status = MCPSessionStatus.ERROR
+                    self.error_message = str(e)
+                    self._ready_event.set()
+                    return
                 if attempt >= self._MAX_RETRIES:
                     self.status = MCPSessionStatus.ERROR
                     self.error_message = f'Failed after {self._MAX_RETRIES + 1} attempts: {e}'

src/langbot/pkg/provider/tools/loaders/mcp_stdio.py

@@ -34,6 +34,11 @@ class MCPSessionErrorPhase(enum.Enum):
     MCP_INIT = 'mcp_init'
     RUNTIME = 'runtime'
     TOOL_CALL = 'tool_call'
+    # Stdio MCP refused because Box is disabled in config or currently
+    # unavailable. Not transient — retries would be pointless. The frontend
+    # uses this phase to render a localized actionable message instead of
+    # the raw RuntimeError text.
+    BOX_UNAVAILABLE = 'box_unavailable'
 
 
 class MCPServerBoxConfig(pydantic.BaseModel):

web/src/app/home/mcp/components/mcp-form/MCPForm.tsx

@@ -78,6 +78,32 @@ function StatusDisplay({
     );
   }
 
+  // Stdio MCP refused because Box is disabled / unreachable. The backend
+  // marks the phase so we can show a localized, actionable message instead
+  // of the raw "box_disabled_in_config" / "box_unavailable" marker.
+  if (runtimeInfo.error_phase === 'box_unavailable') {
+    const isDisabledByConfig =
+      runtimeInfo.error_message === 'box_disabled_in_config';
+    return (
+      <div className="space-y-1">
+        <div className="flex items-center gap-2 text-red-600">
+          <XCircle className="size-5" />
+          <span className="font-medium">{t('mcp.connectionFailed')}</span>
+        </div>
+        <div className="pl-7 text-sm text-red-500 space-y-0.5">
+          <div>
+            {isDisabledByConfig
+              ? t('mcp.boxDisabledStdioRefused')
+              : t('mcp.boxUnavailableStdioRefused')}
+          </div>
+          <div className="text-muted-foreground">
+            {t('mcp.boxStdioRefusedSuggestion')}
+          </div>
+        </div>
+      </div>
+    );
+  }
+
   return (
     <div className="space-y-1">
       <div className="flex items-center gap-2 text-red-600">

web/src/app/home/plugins/mcp-server/mcp-form/MCPFormDialog.tsx

@@ -77,6 +77,32 @@ function StatusDisplay({
     );
   }
 
+  // Stdio MCP refused because Box is disabled / unreachable. The backend
+  // marks the phase so we can show a localized, actionable message instead
+  // of the raw "box_disabled_in_config" / "box_unavailable" marker.
+  if (runtimeInfo.error_phase === 'box_unavailable') {
+    const isDisabledByConfig =
+      runtimeInfo.error_message === 'box_disabled_in_config';
+    return (
+      <div className="space-y-1">
+        <div className="flex items-center gap-2 text-red-600">
+          <XCircle className="w-5 h-5" />
+          <span className="font-medium">{t('mcp.connectionFailed')}</span>
+        </div>
+        <div className="text-sm text-red-500 pl-7 space-y-0.5">
+          <div>
+            {isDisabledByConfig
+              ? t('mcp.boxDisabledStdioRefused')
+              : t('mcp.boxUnavailableStdioRefused')}
+          </div>
+          <div className="text-muted-foreground">
+            {t('mcp.boxStdioRefusedSuggestion')}
+          </div>
+        </div>
+      </div>
+    );
+  }
+
   // 连接失败
   return (
     <div className="space-y-1">

web/src/app/infra/entities/api/index.ts

@@ -529,8 +529,18 @@ export enum MCPSessionStatus {
 export interface MCPServerRuntimeInfo {
   status: MCPSessionStatus;
   error_message?: string;
+  /** Stage at which the session failed. Frontends key off this to render
+   *  a localized actionable message instead of the raw ``error_message``.
+   *  Notable values: ``box_unavailable`` (stdio MCP refused because Box is
+   *  disabled / unreachable). See ``MCPSessionErrorPhase`` (backend). */
+  error_phase?: string;
+  retry_count?: number;
   tool_count: number;
   tools: MCPTool[];
+  /** Optional ``box_session_id`` / ``box_enabled`` set when this stdio
+   *  server runs inside Box. Absent when Box is unavailable. */
+  box_session_id?: string;
+  box_enabled?: boolean;
 }
 
 export type MCPServer =

web/src/i18n/locales/en-US.ts

@@ -738,6 +738,12 @@ const enUS = {
     connectionSuccess: 'Connection successful',
     connectionFailed: 'Connection failed, please check URL',
     connectionFailedStatus: 'Connection Failed',
+    boxDisabledStdioRefused:
+      'Stdio MCP servers require the Box sandbox, which is disabled in config (box.enabled = false).',
+    boxUnavailableStdioRefused:
+      'Stdio MCP servers require the Box sandbox, which is currently unreachable.',
+    boxStdioRefusedSuggestion:
+      'Enable Box (box.enabled = true) and ensure the runtime is healthy, or switch this server to http/sse mode.',
     toolsFound: 'tools',
     unknownError: 'Unknown error',
     noToolsFound: 'No tools found',

web/src/i18n/locales/es-ES.ts

@@ -752,6 +752,12 @@ const esES = {
     connectionSuccess: 'Conexión exitosa',
     connectionFailed: 'Error de conexión, por favor verifica la URL',
     connectionFailedStatus: 'Conexión fallida',
+    boxDisabledStdioRefused:
+      'Los servidores MCP en modo stdio requieren el sandbox de Box, desactivado en la configuración (box.enabled = false).',
+    boxUnavailableStdioRefused:
+      'Los servidores MCP en modo stdio requieren el sandbox de Box, actualmente no accesible.',
+    boxStdioRefusedSuggestion:
+      'Active Box (box.enabled = true) y asegúrese de que el runtime está conectado, o cambie este servidor a modo http/sse.',
     toolsFound: 'herramientas',
     unknownError: 'Error desconocido',
     noToolsFound: 'No se encontraron herramientas',

web/src/i18n/locales/ja-JP.ts

@@ -743,6 +743,12 @@ const jaJP = {
     connectionSuccess: '接続に成功しました',
     connectionFailed: '接続に失敗しました，URLを確認してください',
     connectionFailedStatus: '接続失敗',
+    boxDisabledStdioRefused:
+      'Stdio モードの MCP サーバーは Box サンドボックスを必要としますが、設定で無効化されています（box.enabled = false）。',
+    boxUnavailableStdioRefused:
+      'Stdio モードの MCP サーバーは Box サンドボックスを必要としますが、現在接続できません。',
+    boxStdioRefusedSuggestion:
+      'Box を有効化（box.enabled = true）してランタイムの接続を確認するか、このサーバーを http/sse モードに切り替えてください。',
     toolsFound: '個のツール',
     unknownError: '不明なエラー',
     noToolsFound: 'ツールが見つかりません',

web/src/i18n/locales/ru-RU.ts

@@ -748,6 +748,12 @@ const ruRU = {
     connectionSuccess: 'Подключение успешно',
     connectionFailed: 'Не удалось подключиться, проверьте URL',
     connectionFailedStatus: 'Ошибка подключения',
+    boxDisabledStdioRefused:
+      'MCP-серверы в режиме stdio требуют песочницу Box, которая отключена в конфигурации (box.enabled = false).',
+    boxUnavailableStdioRefused:
+      'MCP-серверы в режиме stdio требуют песочницу Box, которая сейчас недоступна.',
+    boxStdioRefusedSuggestion:
+      'Включите Box (box.enabled = true) и убедитесь, что среда работает, либо переключите этот сервер в режим http/sse.',
     toolsFound: 'инструментов',
     unknownError: 'Неизвестная ошибка',
     noToolsFound: 'Инструменты не найдены',

web/src/i18n/locales/th-TH.ts

@@ -728,6 +728,12 @@ const thTH = {
     connectionSuccess: 'เชื่อมต่อสำเร็จ',
     connectionFailed: 'เชื่อมต่อล้มเหลว กรุณาตรวจสอบ URL',
     connectionFailedStatus: 'เชื่อมต่อล้มเหลว',
+    boxDisabledStdioRefused:
+      'MCP server แบบ stdio ต้องใช้ Sandbox Box ซึ่งถูกปิดใช้งานในการตั้งค่า (box.enabled = false)',
+    boxUnavailableStdioRefused:
+      'MCP server แบบ stdio ต้องใช้ Sandbox Box ซึ่งขณะนี้เชื่อมต่อไม่ได้',
+    boxStdioRefusedSuggestion:
+      'กรุณาเปิดใช้งาน Box (box.enabled = true) และตรวจสอบว่ารันไทม์ทำงานปกติ หรือเปลี่ยน MCP server เป็นโหมด http/sse',
     toolsFound: 'เครื่องมือ',
     unknownError: 'ข้อผิดพลาดที่ไม่ทราบสาเหตุ',
     noToolsFound: 'ไม่พบเครื่องมือ',

web/src/i18n/locales/vi-VN.ts

@@ -742,6 +742,12 @@ const viVN = {
     connectionSuccess: 'Kết nối thành công',
     connectionFailed: 'Kết nối thất bại, vui lòng kiểm tra URL',
     connectionFailedStatus: 'Kết nối thất bại',
+    boxDisabledStdioRefused:
+      'MCP server ở chế độ stdio cần Sandbox Box, hiện đã bị tắt trong cấu hình (box.enabled = false).',
+    boxUnavailableStdioRefused:
+      'MCP server ở chế độ stdio cần Sandbox Box, hiện không thể kết nối.',
+    boxStdioRefusedSuggestion:
+      'Hãy bật Box (box.enabled = true) và đảm bảo runtime hoạt động, hoặc chuyển server này sang chế độ http/sse.',
     toolsFound: 'công cụ',
     unknownError: 'Lỗi không xác định',
     noToolsFound: 'Không tìm thấy công cụ nào',

web/src/i18n/locales/zh-Hans.ts

@@ -710,6 +710,12 @@ const zhHans = {
     connectionSuccess: '连接成功',
     connectionFailed: '连接失败，请检查URL',
     connectionFailedStatus: '连接失败',
+    boxDisabledStdioRefused:
+      'Stdio 模式的 MCP 服务器依赖 Box 沙箱，目前已在配置中禁用（box.enabled = false）。',
+    boxUnavailableStdioRefused:
+      'Stdio 模式的 MCP 服务器依赖 Box 沙箱，目前无法连接。',
+    boxStdioRefusedSuggestion:
+      '请启用 Box（box.enabled = true）并确认运行时连接正常，或将此服务器切换到 http/sse 模式。',
     toolsFound: '个工具',
     unknownError: '未知错误',
     noToolsFound: '未找到任何工具',

web/src/i18n/locales/zh-Hant.ts

@@ -709,6 +709,12 @@ const zhHant = {
     connectionSuccess: '連接成功',
     connectionFailed: '連接失敗，請檢查URL',
     connectionFailedStatus: '連接失敗',
+    boxDisabledStdioRefused:
+      'Stdio 模式的 MCP 伺服器依賴 Box 沙箱，目前已在設定中停用（box.enabled = false）。',
+    boxUnavailableStdioRefused:
+      'Stdio 模式的 MCP 伺服器依賴 Box 沙箱，目前無法連線。',
+    boxStdioRefusedSuggestion:
+      '請啟用 Box（box.enabled = true）並確認執行時連線正常，或將此伺服器切換到 http/sse 模式。',
     toolsFound: '個工具',
     unknownError: '未知錯誤',
     noToolsFound: '未找到任何工具',