We do not have documented usage of @Transactional annotation and how Narayana implementation of the CDI works. We should consider adding it to Narayana or WFLY upstream documentation.
The reason why this issue was created is behaviour which was found by Martin Kouba where Narayana transactional CDI interceptor is not activated when deployment does not contain any @Transacional annotation. This could be a trouble if there is only extension which adds the transactional annotation.
The PR where this was discussed: