Note the icons on the first and last button in the list:
These are the navigation behaviours modified from the defaults. Below, when the last button receives a Down navigation request, you can tell it what to focus on next:
In this case Down leads to the Top button.
If you do the opposite for the top button, you should be able to navigate both ways without ever escaping that vertical box:
Using Explicit also works if the buttons are named. But a custom function allows to intercept the transition if necessary.
Now, if someone told me how to use Wrap there, that’d be swell!