fix(core): guard spec-schema parse for non-spec methods in handler registration

The normalize-then-fall-through change routes custom methods through
_setRequestHandlerByMethod, which previously assumed a spec method
(unconditional getRequestSchema(method).parse). Guard with schema?. so
custom methods registered via Server/Client overrides do not crash.

Author: felixweinberger

packages/core/src/shared/protocol.ts

@@ -1064,7 +1064,7 @@ export abstract class Protocol<ContextT extends BaseContext> {
         this.assertRequestHandlerCapability(method);
         const schema = getRequestSchema(method as RequestMethod);
         this._requestHandlers.set(method, (request, ctx) => {
-            const parsed = schema.parse(request) as Request;
+            const parsed = schema ? (schema.parse(request) as Request) : request;
             return Promise.resolve(handler(parsed, ctx));
         });
     }
@@ -1112,7 +1112,7 @@ export abstract class Protocol<ContextT extends BaseContext> {
         }
         const schema = getNotificationSchema(method as NotificationMethod);
         this._notificationHandlers.set(method, notification => {
-            const parsed = schema.parse(notification);
+            const parsed = schema ? schema.parse(notification) : notification;
             return Promise.resolve(handler(parsed));
         });
     }

packages/server/test/server/setRequestHandlerSchemaParity.test.ts

@@ -1,4 +1,5 @@
 import { describe, expect, it } from 'vitest';
+import { z } from 'zod';
 
 import { CallToolRequestSchema, InMemoryTransport } from '@modelcontextprotocol/core';
 
@@ -46,4 +47,17 @@ describe('Server.setRequestHandler — Zod-schema form parity', () => {
         expect(stringRes.error).toBeDefined();
         expect(schemaRes.error).toEqual(stringRes.error);
     });
+
+    it('schema form handles non-spec methods through Server (no spec-schema crash)', async () => {
+        const Echo = z.object({ method: z.literal('acme/echo'), params: z.object({ msg: z.string() }) });
+        const { ct } = await setup(s => s.setRequestHandler(Echo, req => ({ reply: req.params.msg })));
+        const res = await new Promise<{ result?: unknown; error?: unknown }>(resolve => {
+            ct.onmessage = m => {
+                const msg = m as { result?: unknown; error?: unknown };
+                if ('result' in msg || 'error' in msg) resolve(msg);
+            };
+            ct.send({ jsonrpc: '2.0', id: 1, method: 'acme/echo', params: { msg: 'hi' } });
+        });
+        expect(res.result).toEqual({ reply: 'hi' });
+    });
 });