fix: pass both args when inputSchema omitted in task handler executor

packages/server/src/server/mcp.ts

@@ -1116,7 +1116,9 @@ export type RegisteredTool = {
 /**
  * Creates an executor that invokes the handler with the appropriate arguments.
  * When `inputSchema` is defined, the handler is called with `(args, ctx)`.
- * When `inputSchema` is undefined, the handler is called with just `(ctx)`.
+ * When `inputSchema` is undefined, single-argument callbacks are called with `(ctx)`.
+ * Two-argument callbacks are called with `({}, ctx)` so handlers that need both
+ * values receive the context in the correct argument slot.
  */
 function createToolExecutor(
     inputSchema: StandardSchemaWithJSON | undefined,
@@ -1127,7 +1129,12 @@ function createToolExecutor(
         return async (args, ctx) => callback(args, ctx);
     }
 
-    // When no inputSchema, call with just ctx (the handler expects (ctx) signature)
+    if (handler.length >= 2) {
+        const callback = handler as ToolCallbackInternal;
+        return async (_args, ctx) => callback({}, ctx);
+    }
+
+    // When no inputSchema, one-argument handlers expect just ctx.
     const callback = handler as (ctx: ServerContext) => CallToolResult | Promise<CallToolResult>;
     return async (_args, ctx) => callback(ctx);
 }

test/integration/test/server/mcp.test.ts

@@ -1,5 +1,5 @@
 import { Client } from '@modelcontextprotocol/client';
-import type { Notification, TextContent } from '@modelcontextprotocol/core';
+import type { CallToolResult, Notification, ServerContext, TextContent } from '@modelcontextprotocol/core';
 import { getDisplayName, InMemoryTransport, ProtocolErrorCode, UriTemplate, UrlElicitationRequiredError } from '@modelcontextprotocol/core';
 import { completable, McpServer, ResourceTemplate } from '@modelcontextprotocol/server';
 import { afterEach, beforeEach, describe, expect, test } from 'vitest';
@@ -6282,6 +6282,43 @@ describe('Zod v4', () => {
         });
     });
 
+    test('should pass empty args before context for no-schema two-argument tool callbacks', async () => {
+        const server = new McpServer({
+            name: 'test',
+            version: '1.0.0'
+        });
+
+        const client = new Client({
+            name: 'test-client',
+            version: '1.0.0'
+        });
+
+        let receivedArgs: unknown;
+        let receivedRequestId: unknown;
+
+        const twoArgumentHandler = ((args: unknown, ctx: ServerContext): CallToolResult => {
+            receivedArgs = args;
+            receivedRequestId = ctx.mcpReq.id;
+            return {
+                content: [{ type: 'text' as const, text: 'Success' }]
+            };
+        }) as unknown as (ctx: ServerContext) => CallToolResult;
+
+        server.registerTool('no-schema-two-arg', {}, twoArgumentHandler);
+
+        const [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair();
+        await server.connect(serverTransport);
+        await client.connect(clientTransport);
+
+        const result = await client.callTool({
+            name: 'no-schema-two-arg'
+        });
+
+        expect(result.content).toEqual([{ type: 'text', text: 'Success' }]);
+        expect(receivedArgs).toEqual({});
+        expect(receivedRequestId).toBeDefined();
+    });
+
     // SEP-2663: `taskSupport: 'required'` enforcement and the automatic-polling wrapper
     // depended on the client sending `params.task`. Under the server-directed model the
     // tool handler decides to return `{resultType:'task', task}`; there is no per-tool