I've yet to find an example, but fortunately it seems to work in a pretty straightforward fashion, just working from the KAREL reference manual. This should give me a workaround if I can't resolve the root reboot issue.
Now off to my next problem... when my TP background program is running, UO[3] is on, even when there's no robot "foreground" task active. My KAREL programs don't do this, but I suspect it's b/c I'm using %NOBUSYLAMP in the KAREL programs.
I'm guessing that the header setting BUSY_LAMP_OFF in the TP program would have a similar effect? Still searching my Fanuc manuals for any entries that explain what values do what in that setting, though.
ADDENDUM: Got lucky: tried changing BUSY_LAMP_OFF from 0 to 1, and now when the TP background program is running, UO[3] is still off. This looks like what I need.