When the rest break occurs, I would like it to be able to show the exercises and
such on the screen and blank the screens as usual, but also lock so if the user
walked away from their machine during the break that no other person could
access their workstation.  If the break ends and the user has not returned, stop
showing the exercises and go into a normal screensaver mode (select an available
screensaver to run via configuration or create a screensaver mode within the
application) while still remaining locked.

The reason I suggest running as screensaver is that you can use the screensaver
terminal locking built into the OS.