Improve reporting of error message if cause is known

Extend the reporting of an error over RPC by the cause of the error if it
is known. This then for example not only reports that the signature
verification failed but also the reason, such as when an unsigned file was
found.

Signed-off-by: Stefan Berger <[email protected]>

Author: stefanberger

vllm/v1/engine/core.py

@@ -868,8 +868,11 @@ def _handle_client_request(
                 output.result = UtilityResult(result)
             except BaseException as e:
                 logger.exception("Invocation of %s method failed", method_name)
+                message = str(e)
+                if e.__cause__:
+                    message += f" caused by {e.__cause__}"
                 output.failure_message = (
-                    f"Call to {method_name} method failed: {str(e)}"
+                    f"Call to {method_name} method failed: {message}"
                 )
             self.output_queue.put_nowait(
                 (client_idx, EngineCoreOutputs(utility_output=output))