This has happened twice lately - I'm testing a procedure in Pan X, and I may have programmed myself into an endless loop. Things like this happen during development, no big deal, except: endless beachball, can't get anything to work, can't change screens, can't run anything else, can't Force Quit with the 3-finger salute. Command-period sure doesn't do anything. No choice but to lean on the power button and start over. This is different from the performance drudgery I've talked about with Text Lists, this seems to be specific to running certain procedures "under development." Very inefficient way to debug things.
Is there currently a way to halt a running procedure? If not, is it possible to create such a way?