refactor: inline JSONRPCResponse into JSONRPCMessage during pre-processing

Add inlineJSONRPCResponse() transform that:
1. Replaces JSONRPCResponse with JSONRPCResultResponse | JSONRPCErrorResponse in JSONRPCMessage
2. Removes JSONRPCResponse type alias from generated types

This makes the generated JSONRPCMessage match the local schema structure (4 members),
enabling better type compatibility. JSONRPCResponseSchema remains defined locally
in types.ts as a convenience union.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: ochafik

scripts/generate-schemas.ts

@@ -156,11 +156,15 @@ function preProcessTypes(content: string): string {
     // Transform 4: Update Request.params to use RequestParams
     updateRequestParamsType(sourceFile);
 
-    // Transform 5: Convert JSDoc comments to @description tags for .describe() generation
+    // Transform 5: Inline JSONRPCResponse into JSONRPCMessage and remove JSONRPCResponse
+    // (types.ts will define these locally with proper schema unions)
+    inlineJSONRPCResponse(sourceFile);
+
+    // Transform 6: Convert JSDoc comments to @description tags for .describe() generation
     // (Must run before injectDerivedCapabilityTypes so inline types get @description)
     convertJsDocToDescription(sourceFile);
 
-    // Transform 6: Add derived capability types (extracts from parent interfaces)
+    // Transform 7: Add derived capability types (extracts from parent interfaces)
     injectDerivedCapabilityTypes(sourceFile);
 
     return sourceFile.getFullText();
@@ -284,6 +288,42 @@ function updateRequestParamsType(sourceFile: SourceFile): void {
     }
 }
 
+/**
+ * Inline JSONRPCResponse into JSONRPCMessage and remove JSONRPCResponse type.
+ * This allows types.ts to define these as schema unions locally.
+ *
+ * Transforms:
+ *   type JSONRPCMessage = JSONRPCRequest | JSONRPCNotification | JSONRPCResponse;
+ *   type JSONRPCResponse = JSONRPCResultResponse | JSONRPCErrorResponse;
+ * Into:
+ *   type JSONRPCMessage = JSONRPCRequest | JSONRPCNotification | JSONRPCResultResponse | JSONRPCErrorResponse;
+ *   (JSONRPCResponse removed)
+ */
+function inlineJSONRPCResponse(sourceFile: SourceFile): void {
+    // Find and update JSONRPCMessage
+    const messageType = sourceFile.getTypeAlias('JSONRPCMessage');
+    if (messageType) {
+        const typeNode = messageType.getTypeNode();
+        if (typeNode) {
+            const text = typeNode.getText();
+            // Replace JSONRPCResponse with its components
+            const newType = text.replace(
+                'JSONRPCResponse',
+                'JSONRPCResultResponse | JSONRPCErrorResponse'
+            );
+            messageType.setType(newType);
+            console.log('    ✓ Inlined JSONRPCResponse into JSONRPCMessage');
+        }
+    }
+
+    // Remove JSONRPCResponse type alias
+    const responseType = sourceFile.getTypeAlias('JSONRPCResponse');
+    if (responseType) {
+        responseType.remove();
+        console.log('    ✓ Removed JSONRPCResponse type (defined locally in types.ts)');
+    }
+}
+
 /**
  * Add derived capability types by extracting nested properties from parent interfaces.
  * This creates concrete interface definitions that ts-to-zod can generate schemas for.

src/generated/sdk.schemas.ts

@@ -161,11 +161,6 @@ export const JSONRPCErrorResponseSchema = z
     .strict()
     .describe('A response to a request that indicates an error occurred.');
 
-/** @description A response to a request, containing either the result or error. */
-export const JSONRPCResponseSchema = z
-    .union([JSONRPCResultResponseSchema, JSONRPCErrorResponseSchema])
-    .describe('A response to a request, containing either the result or error.');
-
 /* Empty result */
 /**
  * @description A response that indicates success but carries no data.
@@ -2428,7 +2423,7 @@ To update this file, run: npm run fetch:spec-types */ /* JSON-RPC types */
  * @category JSON-RPC
  */
 export const JSONRPCMessageSchema = z
-    .union([JSONRPCRequestSchema, JSONRPCNotificationSchema, JSONRPCResponseSchema])
+    .union([JSONRPCRequestSchema, JSONRPCNotificationSchema, JSONRPCResultResponseSchema, JSONRPCErrorResponseSchema])
     .describe(
         'This file is automatically generated from the Model Context Protocol specification.\n\nSource: https://github.com/modelcontextprotocol/modelcontextprotocol\nPulled from: https://raw.githubusercontent.com/modelcontextprotocol/modelcontextprotocol/main/schema/draft/schema.ts\nLast updated from commit: 35fa160caf287a9c48696e3ae452c0645c713669\n\nDO NOT EDIT THIS FILE MANUALLY. Changes will be overwritten by automated updates.\nTo update this file, run: npm run fetch:spec-types'
     );

src/generated/sdk.types.ts

@@ -17,7 +17,7 @@
  *
  * @category JSON-RPC
  */
-export type JSONRPCMessage = JSONRPCRequest | JSONRPCNotification | JSONRPCResponse;
+export type JSONRPCMessage = JSONRPCRequest | JSONRPCNotification | JSONRPCResultResponse | JSONRPCErrorResponse;
 
 /** @internal */
 export const LATEST_PROTOCOL_VERSION = 'DRAFT-2026-v1';
@@ -150,9 +150,6 @@ export interface JSONRPCErrorResponse {
     error: Error;
 }
 
-/** @description A response to a request, containing either the result or error. */
-export type JSONRPCResponse = JSONRPCResultResponse | JSONRPCErrorResponse;
-
 // Standard JSON-RPC error codes
 export const PARSE_ERROR = -32700;
 export const INVALID_REQUEST = -32600;

src/types.ts

@@ -197,8 +197,6 @@ import {
     // Derived capability schemas (generated from extracted types)
     ClientTasksCapabilitySchema,
     ServerTasksCapabilitySchema,
-    // JSON-RPC schemas
-    JSONRPCResponseSchema,
     // Progress
     ProgressNotificationParamsSchema,
 } from './generated/sdk.schemas.js';
@@ -343,7 +341,6 @@ export {
     SamplingMessageContentBlockSchema,
     ClientTasksCapabilitySchema,
     ServerTasksCapabilitySchema,
-    JSONRPCResponseSchema,
     ProgressNotificationParamsSchema,
 };
 
@@ -421,14 +418,15 @@ export enum ErrorCode {
     UrlElicitationRequired = -32042
 }
 
+export const JSONRPCResponseSchema = z.union([JSONRPCResultResponseSchema, JSONRPCErrorResponseSchema]);
+
 export const JSONRPCMessageSchema = z.union([
     JSONRPCRequestSchema,
     JSONRPCNotificationSchema,
     JSONRPCResultResponseSchema,
     JSONRPCErrorResponseSchema
 ]);
 
-
 /* Cancellation */
 /**
  * This notification can be sent by either side to indicate that it is cancelling a previously-issued request.