chore: mcp code tool explicit error message when missing a run function

Author: stainless-app[bot]

packages/mcp-server/package.json

@@ -38,6 +38,7 @@
     "express": "^5.1.0",
     "jq-web": "https://github.com/stainless-api/jq-web/releases/download/v0.8.6/jq-web.tar.gz",
     "qs": "^6.14.0",
+    "typescript": "5.8.3",
     "yargs": "^17.7.2",
     "zod": "^3.25.20",
     "zod-to-json-schema": "^3.24.5",
@@ -64,8 +65,7 @@
     "ts-morph": "^19.0.0",
     "ts-node": "^10.5.0",
     "tsc-multi": "https://github.com/stainless-api/tsc-multi/releases/download/v1.1.9/tsc-multi.tgz",
-    "tsconfig-paths": "^4.0.0",
-    "typescript": "5.8.3"
+    "tsconfig-paths": "^4.0.0"
   },
   "imports": {
     "cas-parser-node-mcp": ".",

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

@@ -1,11 +1,58 @@
 // File generated from our OpenAPI spec by Stainless. See CONTRIBUTING.md for details.
 
 import util from 'node:util';
+
+import ts from 'typescript';
+
 import { WorkerInput, WorkerSuccess, WorkerError } from './code-tool-types';
 import { CasParser } from 'cas-parser-node';
 
+function getRunFunctionNode(
+  code: string,
+): ts.FunctionDeclaration | ts.FunctionExpression | ts.ArrowFunction | null {
+  const sourceFile = ts.createSourceFile('code.ts', code, ts.ScriptTarget.Latest, true);
+
+  for (const statement of sourceFile.statements) {
+    // Check for top-level function declarations
+    if (ts.isFunctionDeclaration(statement)) {
+      if (statement.name?.text === 'run') {
+        return statement;
+      }
+    }
+
+    // Check for variable declarations: const run = () => {} or const run = function() {}
+    if (ts.isVariableStatement(statement)) {
+      for (const declaration of statement.declarationList.declarations) {
+        if (ts.isIdentifier(declaration.name) && declaration.name.text === 'run') {
+          // Check if it's initialized with a function
+          if (
+            declaration.initializer &&
+            (ts.isFunctionExpression(declaration.initializer) || ts.isArrowFunction(declaration.initializer))
+          ) {
+            return declaration.initializer;
+          }
+        }
+      }
+    }
+  }
+
+  return null;
+}
+
 const fetch = async (req: Request): Promise<Response> => {
   const { opts, code } = (await req.json()) as WorkerInput;
+
+  const runFunctionNode = getRunFunctionNode(code);
+  if (!runFunctionNode) {
+    return Response.json(
+      {
+        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```',
+      } satisfies WorkerError,
+      { status: 400, statusText: 'Code execution error' },
+    );
+  }
+
   const client = new CasParser({
     ...opts,
   });