fix(mcp): rebind cached tools to connected server (#195) (#223)

Author: vrtnis

.changeset/funny-dragons-tell.md

@@ -0,0 +1,5 @@
+---
+'@openai/agents-core': patch
+---
+
+Rebinds cached tools to the current MCP server to avoid stale tool invocation (fixes #195)

packages/agents-core/src/mcp.ts

@@ -219,7 +219,7 @@ export async function getAllMcpFunctionTools<TContext = UnknownContext>(
   return allTools;
 }
 
-const _cachedTools: Record<string, FunctionTool<any, any, unknown>[]> = {};
+const _cachedTools: Record<string, MCPTool[]> = {};
 /**
  * Remove cached tools for the given server so the next lookup fetches fresh data.
  *
@@ -236,7 +236,9 @@ async function getFunctionToolsFromServer<TContext = UnknownContext>(
   convertSchemasToStrict: boolean,
 ): Promise<FunctionTool<TContext, any, unknown>[]> {
   if (server.cacheToolsList && _cachedTools[server.name]) {
-    return _cachedTools[server.name];
+    return _cachedTools[server.name].map((t) =>
+      mcpToFunctionTool(t, server, convertSchemasToStrict),
+    );
   }
   return withMCPListToolsSpan(
     async (span) => {
@@ -246,7 +248,7 @@ async function getFunctionToolsFromServer<TContext = UnknownContext>(
         mcpToFunctionTool(t, server, convertSchemasToStrict),
       );
       if (server.cacheToolsList) {
-        _cachedTools[server.name] = tools;
+        _cachedTools[server.name] = mcpTools;
       }
       return tools;
     },

packages/agents-core/test/mcpCache.test.ts

@@ -1,5 +1,6 @@
 import { describe, it, expect } from 'vitest';
 import { getAllMcpTools } from '../src/mcp';
+import type { FunctionTool } from '../src/tool';
 import { withTrace } from '../src/tracing';
 import { NodeMCPServerStdio } from '../src/shims/mcp-server/node';
 import type { CallToolResultContent } from '../src/mcp';
@@ -60,4 +61,31 @@ describe('MCP tools cache invalidation', () => {
       expect(tools.map((t) => t.name)).toEqual(['b']);
     });
   });
+
+  it('binds cached tools to the current server instance', async () => {
+    await withTrace('test', async () => {
+      const tools = [
+        {
+          name: 'a',
+          description: '',
+          inputSchema: { type: 'object', properties: {} },
+        },
+      ];
+
+      const serverA = new StubServer('server', tools);
+      await getAllMcpTools([serverA]);
+
+      const serverB = new StubServer('server', tools);
+      let called = false;
+      (serverB as any).callTool = async () => {
+        called = true;
+        return [];
+      };
+
+      const cachedTools = (await getAllMcpTools([serverB])) as FunctionTool[];
+      await cachedTools[0].invoke({} as any, '{}');
+
+      expect(called).toBe(true);
+    });
+  });
 });