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

#2006)

* Prevent sending response headers if already sent in default error handler

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.

* Update log messages as per code review feedback

src/receivers/HTTPModuleFunctions.ts

@@ -190,6 +190,14 @@ 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('An unhandled error occurred after ack() called in a listener');
+      logger.debug(`Error details: ${error}, storedResponse: ${storedResponse}`);
+      return false;
+    }
+
     if ('code' in error) {
     // CodedError has code: string
       const errorCode = (error as CodedError).code;