Improve generic 'Method not found' message for better debuggability

Co-Authored-By: Claude <noreply@anthropic.com>

Author: alantriesagain

packages/core/src/shared/protocol.ts

@@ -689,7 +689,7 @@ export abstract class Protocol<SendRequestT extends Request, SendNotificationT e
                 id: request.id,
                 error: {
                     code: ErrorCode.MethodNotFound,
-                    message: 'Method not found'
+                    message: `Method '${request.method}' not found`
                 }
             };
 

test/integration/test/server.test.ts

@@ -2392,7 +2392,7 @@ describe('Task-based execution', () => {
 
         // Try to get a task when server doesn't have TaskStore
         // The server will return a "Method not found" error
-        await expect(client.experimental.tasks.getTask('non-existent')).rejects.toThrow('Method not found');
+        await expect(client.experimental.tasks.getTask('non-existent')).rejects.toThrow("Method 'tasks/get' not found");
     });
 
     test('should automatically attach related-task metadata to nested requests during tool execution', async () => {