fix: dispatch callback failing on probe [LET-5606] (#5541)

* probe

* cleanup

* hi

* log

---------

Co-authored-by: Letta Bot <noreply@letta.com>

letta/services/run_manager.py

@@ -272,7 +272,7 @@ class RunManager:
                 log_event("POST callback finished")
                 result["callback_status_code"] = resp.status_code
         except Exception as e:
-            error_message = f"Failed to dispatch callback for run {callback_info['run_id']} to {callback_info['callback_url']}: {e!s}"
+            error_message = f"Failed to dispatch callback for run {callback_info['run_id']} to {callback_info['callback_url']}: {e!r}"
             logger.error(error_message)
             result["callback_error"] = error_message
             # Continue silently - callback failures should not affect run completion