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/cas-generator/generate-cas-cas-generator.ts

@@ -1,7 +1,7 @@
 // File generated from our OpenAPI spec by Stainless. See CONTRIBUTING.md for details.
 
-import { maybeFilter } from 'cas-parser-node-mcp/filtering';
-import { Metadata, asTextContentResult } from 'cas-parser-node-mcp/tools/types';
+import { isJqError, maybeFilter } from 'cas-parser-node-mcp/filtering';
+import { Metadata, asErrorResult, asTextContentResult } from 'cas-parser-node-mcp/tools/types';
 
 import { Tool } from '@modelcontextprotocol/sdk/types.js';
 import CasParser from 'cas-parser-node';
@@ -61,7 +61,14 @@ export const tool: Tool = {
 
 export const handler = async (client: CasParser, args: Record<string, unknown> | undefined) => {
   const { jq_filter, ...body } = args as any;
-  return asTextContentResult(await maybeFilter(jq_filter, await client.casGenerator.generateCas(body)));
+  try {
+    return asTextContentResult(await maybeFilter(jq_filter, await client.casGenerator.generateCas(body)));
+  } catch (error) {
+    if (isJqError(error)) {
+      return asErrorResult(error.message);
+    }
+    throw error;
+  }
 };
 
 export default { metadata, tool, handler };

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';