fix(converge): nits r0-003/004/007/008 — error-code semantics, codemod ref, negative-result test

Author: felixweinberger

docs/migration.md

@@ -393,8 +393,6 @@ server.setRequestHandler('acme/search', { params: SearchParams, result: SearchRe
 
 The handler receives the parsed `params` directly (not the full request envelope). `_meta` is stripped before validation and is available as `ctx.mcpReq._meta`. Supplying `result` types the handler's return value; omit it to return any `Result`.
 
-The codemod handles this rewrite for both spec and custom methods.
-
 #### Sending custom-method requests
 
 `request()` and `ctx.mcpReq.send()` now accept an optional result schema for custom methods:

packages/core/src/shared/protocol.ts

@@ -916,7 +916,7 @@ export abstract class Protocol<ContextT extends BaseContext> {
                         resolve(parseResult.data);
                     } else {
                         reject(
-                            new ProtocolError(ProtocolErrorCode.InvalidParams, `Invalid result for ${request.method}: ${parseResult.error}`)
+                            new ProtocolError(ProtocolErrorCode.InternalError, `Invalid result for ${request.method}: ${parseResult.error}`)
                         );
                     }
                 }, reject);
@@ -1162,7 +1162,7 @@ export abstract class Protocol<ContextT extends BaseContext> {
                 delete userParams._meta;
                 const parsed = await validateStandardSchema(schemas.params, userParams);
                 if (!parsed.success) {
-                    throw new Error(`Invalid params for notification ${method}: ${parsed.error}`);
+                    throw new ProtocolError(ProtocolErrorCode.InvalidParams, `Invalid params for notification ${method}: ${parsed.error}`);
                 }
                 await handler(parsed.data);
             });

packages/core/test/shared/customMethods.test.ts

@@ -3,7 +3,7 @@ import { z } from 'zod/v4';
 
 import { Protocol } from '../../src/shared/protocol.js';
 import type { BaseContext, JSONRPCRequest, Result } from '../../src/exports/public/index.js';
-import { ProtocolError } from '../../src/types/index.js';
+import { ProtocolError, ProtocolErrorCode } from '../../src/types/index.js';
 import { InMemoryTransport } from '../../src/util/inMemory.js';
 
 class TestProtocol extends Protocol<BaseContext> {
@@ -127,6 +127,15 @@ describe('Protocol custom-method support', () => {
             const [a] = await pair();
             expect(() => a.request({ method: 'acme/unknown' } as never)).toThrow(TypeError);
         });
+
+        it('rejects with ProtocolError(InternalError) when the response fails the result schema', async () => {
+            const [a, b] = await pair();
+            b.setRequestHandler('acme/bad', { params: z.object({}) }, async () => ({ wrong: 123 }));
+
+            await expect(a.request({ method: 'acme/bad', params: {} }, z.object({ echoed: z.string() }))).rejects.toMatchObject({
+                code: ProtocolErrorCode.InternalError
+            });
+        });
     });
 
     describe('ctx.mcpReq.send schema overload', () => {