Hi @washcycle!
Interesting use case! I found a similar old post. While it was in Jupyter, the same idea should apply:
I have a Mac and found these commands to work (granted I manually grabbed the PID to be safe):
# find <PIDProdigy> for prodigy session
ps -A | grep prodigy
# kill PID
kill -9 <PIDProdigy>
Let me know if this helps or if you have any other questions!