From f6f0c6e023d3b50c7ee05a7db260472302eebe67 Mon Sep 17 00:00:00 2001
From: Andrew Harvard <aharvard@squareup.com>
Date: Thu, 19 Feb 2026 15:57:53 -0500
Subject: [PATCH] fix(apps): restore MCP app sampling support reverted by #6933
 (#7366)

---
 .../src/components/McpApps/McpAppRenderer.tsx | 49 ++++++++++++++++++-
 1 file changed, 47 insertions(+), 2 deletions(-)

diff --git a/ui/desktop/src/components/McpApps/McpAppRenderer.tsx b/ui/desktop/src/components/McpApps/McpAppRenderer.tsx
index 4733727359..cd1646fcbb 100644
--- a/ui/desktop/src/components/McpApps/McpAppRenderer.tsx
+++ b/ui/desktop/src/components/McpApps/McpAppRenderer.tsx
@@ -15,7 +15,7 @@
  * - "standalone" — Goose-specific mode for dedicated Electron windows
  */
 
-import { AppRenderer } from '@mcp-ui/client';
+import { AppRenderer, type RequestHandlerExtra } from '@mcp-ui/client';
 import type {
   McpUiDisplayMode,
   McpUiHostContext,
@@ -23,7 +23,7 @@ import type {
   McpUiResourcePermissions,
   McpUiSizeChangedNotification,
 } from '@modelcontextprotocol/ext-apps/app-bridge';
-import type { CallToolResult } from '@modelcontextprotocol/sdk/types.js';
+import type { CallToolResult, JSONRPCRequest } from '@modelcontextprotocol/sdk/types.js';
 import { useCallback, useEffect, useMemo, useReducer, useRef, useState } from 'react';
 import { callTool, readResource } from '../../api';
 import { AppEvents } from '../../constants/events';
@@ -40,6 +40,8 @@ import {
   McpAppToolInputPartial,
   McpAppToolResult,
   DimensionLayout,
+  SamplingCreateMessageParams,
+  SamplingCreateMessageResponse,
 } from './types';
 
 const DEFAULT_IFRAME_HEIGHT = 200;
@@ -265,7 +267,13 @@ export default function McpAppRenderer({
   const containerRef = useRef<HTMLDivElement>(null);
   const [containerWidth, setContainerWidth] = useState<number>(0);
   const [containerHeight, setContainerHeight] = useState<number>(0);
+  const [apiHost, setApiHost] = useState<string | null>(null);
+  const [secretKey, setSecretKey] = useState<string | null>(null);
 
+  useEffect(() => {
+    window.electron.getGoosedHostPort().then(setApiHost);
+    window.electron.getSecretKey().then(setSecretKey);
+  }, []);
 
   // Fetch the resource from the extension to get HTML and metadata (CSP, permissions, etc.).
   // If cachedHtml is provided we show it immediately; the fetch updates metadata and
@@ -527,6 +535,42 @@ export default function McpAppRenderer({
     return () => observer.disconnect();
   }, []);
 
+  const handleFallbackRequest = useCallback(
+    async (request: JSONRPCRequest, _extra: RequestHandlerExtra) => {
+      if (request.method === 'sampling/createMessage') {
+        if (!sessionId || !apiHost || !secretKey) {
+          throw new Error('Session not initialized for sampling request');
+        }
+        const { messages, systemPrompt, maxTokens } =
+          request.params as unknown as SamplingCreateMessageParams;
+        const response = await fetch(`${apiHost}/sessions/${sessionId}/sampling/message`, {
+          method: 'POST',
+          headers: {
+            'Content-Type': 'application/json',
+            'X-Secret-Key': secretKey,
+          },
+          body: JSON.stringify({
+            messages: messages.map((m) => ({
+              role: m.role,
+              content: m.content,
+            })),
+            systemPrompt,
+            maxTokens,
+          }),
+        });
+        if (!response.ok) {
+          throw new Error(`Sampling request failed: ${response.statusText}`);
+        }
+        return (await response.json()) as SamplingCreateMessageResponse;
+      }
+      return {
+        status: 'error' as const,
+        message: `Unhandled JSON-RPC method: ${request.method ?? '<unknown>'}`,
+      };
+    },
+    [sessionId, apiHost, secretKey]
+  );
+
   const handleError = useCallback((err: Error) => {
     console.error('[MCP App Error]:', err);
     dispatch({ type: 'ERROR', message: errorMessage(err) });
@@ -643,6 +687,7 @@ export default function McpAppRenderer({
         onReadResource={handleReadResource}
         onLoggingMessage={handleLoggingMessage}
         onSizeChanged={handleSizeChanged}
+        onFallbackRequest={handleFallbackRequest}
         onError={handleError}
       />
     );