fix: response result-schema mismatch throws SdkError(InvalidResult) instead of ProtocolError(InternalError)

Author: felixweinberger

.changeset/custom-methods-minimal.md

@@ -6,4 +6,4 @@
 
 Add custom (non-spec) method support: a 3-arg `setRequestHandler(method, schemas, handler)` / `setNotificationHandler(method, schemas, handler)` form for vendor-prefixed methods, and a `request(req, resultSchema)` overload (also on `ctx.mcpReq.send`) for typed custom-method results. Spec-method calls are unchanged.
 
-Response result-schema validation failure now rejects with `ProtocolError(InternalError)` instead of a raw `ZodError`.
+Response result-schema validation failure now rejects with `SdkError(InvalidResult)` instead of a raw `ZodError`. Adds `SdkErrorCode.InvalidResult`.

packages/core/src/errors/sdkErrors.ts

@@ -26,6 +26,8 @@ export enum SdkErrorCode {
     ConnectionClosed = 'CONNECTION_CLOSED',
     /** Failed to send message */
     SendFailed = 'SEND_FAILED',
+    /** Response result failed local schema validation */
+    InvalidResult = 'INVALID_RESULT',
 
     // Transport errors
     ClientHttpNotImplemented = 'CLIENT_HTTP_NOT_IMPLEMENTED',

packages/core/src/shared/protocol.ts

@@ -925,9 +925,7 @@ export abstract class Protocol<ContextT extends BaseContext> {
                     if (parseResult.success) {
                         resolve(parseResult.data);
                     } else {
-                        reject(
-                            new ProtocolError(ProtocolErrorCode.InternalError, `Invalid result for ${request.method}: ${parseResult.error}`)
-                        );
+                        reject(new SdkError(SdkErrorCode.InvalidResult, `Invalid result for ${request.method}: ${parseResult.error}`));
                     }
                 }, reject);
             });

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

@@ -3,7 +3,8 @@ import { z } from 'zod/v4';
 
 import { Protocol } from '../../src/shared/protocol.js';
 import type { BaseContext, JSONRPCRequest, Result, StandardSchemaV1 } from '../../src/exports/public/index.js';
-import { ProtocolError, ProtocolErrorCode } from '../../src/types/index.js';
+import { ProtocolError } from '../../src/types/index.js';
+import { SdkErrorCode } from '../../src/errors/sdkErrors.js';
 import { InMemoryTransport } from '../../src/util/inMemory.js';
 
 class TestProtocol extends Protocol<BaseContext> {
@@ -142,12 +143,12 @@ describe('Protocol custom-method support', () => {
             expect(() => a.request({ method: 'acme/unknown' } as never)).toThrow(TypeError);
         });
 
-        it('rejects with ProtocolError(InternalError) when the response fails the result schema', async () => {
+        it('rejects with SdkError(InvalidResult) 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
+                code: SdkErrorCode.InvalidResult
             });
         });