chore(internal): show error causes in MCP servers when running in local mode

Author: stainless-app[bot]

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

@@ -189,7 +189,8 @@ function makeSdkProxy<T extends object>(obj: T, { path, isBelievedBad = false }:
 
 function parseError(code: string, error: unknown): string | undefined {
   if (!(error instanceof Error)) return;
-  const message = error.name ? `${error.name}: ${error.message}` : error.message;
+  const cause = error.cause instanceof Error ? `: ${error.cause.message}` : '';
+  const message = error.name ? `${error.name}: ${error.message}${cause}` : `${error.message}${cause}`;
   try {
     // Deno uses V8; the first "<anonymous>:LINE:COLUMN" is the top of stack.
     const lineNumber = error.stack?.match(/<anonymous>:([0-9]+):[0-9]+/)?.[1];