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>

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 =