Prevent sending response headers if already sent in default error han…

…dler

This change addresses a bug where the defaultProcessEventErrorHandler
could attempt to send HTTP response headers after they've already been
sent, leading to a server error. The fix adds a check for the
response.headersSent property before attempting to write headers or
end the response.

The update ensures that the error handler behaves correctly even if
ack() has been called previously during request processing.

src/receivers/HTTPModuleFunctions.ts

@@ -190,6 +190,13 @@ export class HTTPModuleFunctions {
     args: ReceiverProcessEventErrorHandlerArgs,
   ): Promise<boolean> {
     const { error, response, logger, storedResponse } = args;
+
+    // Check if the response headers have already been sent
+    if (response.headersSent) {
+      logger.error('Headers already sent, cannot send another response');
+      return false;
+    }
+
     if ('code' in error) {
     // CodedError has code: string
       const errorCode = (error as CodedError).code;