Per-message event handling
After the basket has received the command to add a product in it, the web application will not yet be updated with the new basket information.
In terms of responsibility, it is correct that a command handler does not update the UI. Instead it has the responsibility of notifying that a product was added into the basket, and that the total and the content have changed.
This is an important concept for evolutional software. Events are a great way of decoupling, not only on actual features, but also with future, hypothetical features. If in future there is a need for another feature depending on how the basket updated, then none of the existing code would be affected as just another worker would be necessary to generate another answer to the event.
Because many (more than one) can be interested in an event, the service bus queue is not the correct solution, as it is designed around the idea that with competing consumers, only one receives the message. A variation on this...
