Where are the program bounds stored?

They are calculated by the backplot previewer, which is why they are only in glcannon. The GUIs that don't do a backplot don't have any idea that the g-code is out of bounds until it is too late. (Touchy, for example, does not give an out-of-bounds warning at program load)

I guess the problem with having it in the status is that the data will often simply not exist.

QtPlasmaC does something similar to check for A. if the program is outside the work envelope (bounding box), and B. let the user know how far outside the bounds the program is.  I would imagine it could be adapted to do what you're after.

I am not sure how familiar you are with Python, but you can check it out here:  github.com/LinuxCNC/linuxcnc/blob/master...qtplasmac_handler.py

you're looking for:  def bounds_check