Woohoo privesc progress… thanks to reviewing the info I already have, plus some more enumeration, plus some trivial binary arithmetic.
Edit: squeeeeeee! I got root! Holy cow that was a lot of learning. It’s going to take me a couple of hours to complete my writeup on this one, and I’ll be adding to my personal list of useful tools and tips in about 3 different sections. This box was definitely worth trying harder on.