fix(mcp): return tool execution error on jq failure

Author: stainless-app[bot]

packages/mcp-server/src/filtering.ts

@@ -12,3 +12,7 @@ export async function maybeFilter(jqFilter: unknown | undefined, response: any):
 async function jq(json: any, jqFilter: string) {
   return (await initJq).json(json, jqFilter);
 }
+
+export function isJqError(error: any): error is Error {
+  return error instanceof Error && 'stderr' in error;
+}

packages/mcp-server/src/tools/types.ts

@@ -87,6 +87,18 @@ export async function asBinaryContentResult(response: Response): Promise<ToolCal
   }
 }
 
+export function asErrorResult(message: string): ToolCallResult {
+  return {
+    content: [
+      {
+        type: 'text',
+        text: message,
+      },
+    ],
+    isError: true,
+  };
+}
+
 export type Metadata = {
   resource: string;
   operation: 'read' | 'write';