feat(mcp): return logs on code tool errors

Author: stainless-app[bot]

packages/mcp-server/src/code-tool-types.ts

@@ -11,4 +11,8 @@ export type WorkerSuccess = {
   logLines: string[];
   errLines: string[];
 };
-export type WorkerError = { message: string | undefined };
+export type WorkerError = {
+  message: string | undefined;
+  logLines: string[];
+  errLines: string[];
+};

packages/mcp-server/src/code-tool-worker.ts

@@ -146,6 +146,8 @@ const fetch = async (req: Request): Promise<Response> => {
       {
         message:
           'The code param is missing. Provide one containing a top-level `run` function. Write code within this template:\n\n```\nasync function run(client) {\n  // Fill this out\n}\n```',
+        logLines: [],
+        errLines: [],
       } satisfies WorkerError,
       { status: 400, statusText: 'Code execution error' },
     );
@@ -157,6 +159,8 @@ const fetch = async (req: Request): Promise<Response> => {
       {
         message:
           'The code is missing a top-level `run` function. Write code within this template:\n\n```\nasync function run(client) {\n  // Fill this out\n}\n```',
+        logLines: [],
+        errLines: [],
       } satisfies WorkerError,
       { status: 400, statusText: 'Code execution error' },
     );
@@ -189,6 +193,8 @@ const fetch = async (req: Request): Promise<Response> => {
     return Response.json(
       {
         message: parseError(code, e),
+        logLines,
+        errLines,
       } satisfies WorkerError,
       { status: 400, statusText: 'Code execution error' },
     );

packages/mcp-server/src/code-tool.ts

@@ -132,9 +132,30 @@ export async function codeTool(): Promise<Endpoint> {
           content: [returnOutput, logOutput, errOutput].filter((block) => block !== null),
         };
       } else {
-        const { message } = (await resp.json()) as WorkerError;
+        const { message, logLines, errLines } = (await resp.json()) as WorkerError;
+        const messageOutput: ContentBlock | null =
+          message == null ? null : (
+            {
+              type: 'text',
+              text: message,
+            }
+          );
+        const logOutput: ContentBlock | null =
+          logLines.length === 0 ?
+            null
+          : {
+              type: 'text',
+              text: logLines.join('\n'),
+            };
+        const errOutput: ContentBlock | null =
+          errLines.length === 0 ?
+            null
+          : {
+              type: 'text',
+              text: 'Error output:\n' + errLines.join('\n'),
+            };
         return {
-          content: message == null ? [] : [{ type: 'text', text: message }],
+          content: [messageOutput, logOutput, errOutput].filter((block) => block !== null),
           isError: true,
         };
       }