fix: prevent infinite loop of tool-input notifications in MCP Apps (#6374)

ui/desktop/src/components/McpApps/useSandboxBridge.ts

@@ -86,6 +86,21 @@ export function useSandboxBridge(options: SandboxBridgeOptions): SandboxBridgeRe
 
           case 'ui/notifications/initialized':
             isGuestInitializedRef.current = true;
+            // Send any pending tool data that arrived before initialization
+            if (toolInput) {
+              sendToSandbox({
+                jsonrpc: '2.0',
+                method: 'ui/notifications/tool-input',
+                params: { arguments: toolInput.arguments },
+              });
+            }
+            if (toolResult) {
+              sendToSandbox({
+                jsonrpc: '2.0',
+                method: 'ui/notifications/tool-result',
+                params: toolResult,
+              });
+            }
             break;
 
           case 'ui/notifications/size-changed': {
@@ -163,7 +178,16 @@ export function useSandboxBridge(options: SandboxBridgeOptions): SandboxBridgeRe
         }
       }
     },
-    [resourceHtml, resourceCsp, resolvedTheme, sendToSandbox, onMcpRequest, onSizeChanged]
+    [
+      resourceHtml,
+      resourceCsp,
+      resolvedTheme,
+      sendToSandbox,
+      onMcpRequest,
+      onSizeChanged,
+      toolInput,
+      toolResult,
+    ]
   );
 
   useEffect(() => {

ui/desktop/src/components/ToolCallWithResponse.tsx

@@ -1,6 +1,6 @@
 import { ToolIconWithStatus, ToolCallStatus } from './ToolCallStatusIndicator';
 import { getToolCallIcon } from '../utils/toolIconMapping';
-import React, { useEffect, useRef, useState } from 'react';
+import React, { useEffect, useRef, useState, useMemo } from 'react';
 import { Button } from './ui/button';
 import { ToolCallArguments, ToolCallArgumentValue } from './ToolCallArguments';
 import MarkdownContent from './MarkdownContent';
@@ -71,12 +71,19 @@ function isEmbeddedResource(content: Content): content is EmbeddedResource {
   return 'resource' in content && typeof (content as Record<string, unknown>).resource === 'object';
 }
 
-function maybeRenderMCPApp(
+interface McpAppWrapperProps {
-  toolRequest: ToolRequestMessageContent,
+  toolRequest: ToolRequestMessageContent;
-  toolResponse: ToolResponseMessageContent | undefined,
+  toolResponse?: ToolResponseMessageContent;
-  sessionId: string,
+  sessionId: string;
-  append?: (value: string) => void
+  append?: (value: string) => void;
-): React.ReactNode {
+}
+
+function McpAppWrapper({
+  toolRequest,
+  toolResponse,
+  sessionId,
+  append,
+}: McpAppWrapperProps): React.ReactNode {
   const requestWithMeta = toolRequest as ToolRequestWithMeta;
   let resourceUri = requestWithMeta._meta?.['ui/resourceUri'];
 
@@ -87,24 +94,37 @@ function maybeRenderMCPApp(
     }
   }
 
-  if (!resourceUri) return null;
+  const extensionName =
-  if (requestWithMeta.toolCall.status !== 'success') return null;
+    requestWithMeta.toolCall.status === 'success'
+      ? requestWithMeta.toolCall.value.name.split('__')[0]
+      : '';
 
-  const extensionName = requestWithMeta.toolCall.value.name.split('__')[0];
+  const toolArguments =
+    requestWithMeta.toolCall.status === 'success'
+      ? requestWithMeta.toolCall.value.arguments
+      : undefined;
 
-  let toolResult: CallToolResponse | undefined;
+  // Memoize toolInput to prevent unnecessary re-renders
-  if (toolResponse) {
+  const toolInput = useMemo(() => ({ arguments: toolArguments || {} }), [toolArguments]);
+
+  // Memoize toolResult to prevent unnecessary re-renders
+  const toolResult = useMemo(() => {
+    if (!toolResponse) return undefined;
     const resultWithMeta = toolResponse.toolResult as ToolResultWithMeta;
     if (resultWithMeta?.status === 'success' && resultWithMeta.value) {
-      toolResult = resultWithMeta.value;
+      return resultWithMeta.value;
     }
-  }
+    return undefined;
+  }, [toolResponse]);
+
+  if (!resourceUri) return null;
+  if (requestWithMeta.toolCall.status !== 'success') return null;
 
   return (
     <div className="mt-3">
       <McpAppRenderer
         resourceUri={resourceUri}
-        toolInput={{ arguments: requestWithMeta.toolCall.value.arguments || {} }}
+        toolInput={toolInput}
         toolResult={toolResult}
         extensionName={extensionName}
         sessionId={sessionId}
@@ -181,7 +201,14 @@ export default function ToolCallWithResponse({
           }
         })}
 
-      {sessionId && maybeRenderMCPApp(toolRequest, toolResponse, sessionId, append)}
+      {sessionId && (
+        <McpAppWrapper
+          toolRequest={toolRequest}
+          toolResponse={toolResponse}
+          sessionId={sessionId}
+          append={append}
+        />
+      )}
     </>
   );
 }