What is "stage transactionality"? If I do a Google search for it, I just find this page.
If you read a few more pages, then it should hopefully become clearer. This page is specifically talking about it: https://mats3.io/using-mats/transactions-and-redelivery/ - but as it is one of the primary points of why I made Mats, it is mentioned multiple places, e.g. here: https://mats3.io/background/what-is-mats/
This is not Mats-specific - it is directly using functionality provided by the message broker, via JMS.
What is "stage transactionality"? If I do a Google search for it, I just find this page.