Oh $%^#, I made it worse.
I stripped something in the toilet's shut-off valve -- I'm hoping all I've damaged is the plastic handle. And, of course, I've now got no idea whether getting the plastic nut on the underside of the tank to turn did any good or not.
Gonna take a break, calm down, come back to it and see if I can tell whether all I broke was the handle or not, attempt a kludge and/or try to find a replacement if so, and then decide whether to ask a less plumbing-klutzy friend to do me a big favour, based on whether it turns out that I improved anything before I broke things.
I should not be so easily defeated by something so primitive, considering the more complicated stuff that I can deal with.
I was going to try to fix the shower today as well, but I'm wondering whether that'd just be asking for trouble.
Grumpy now. *pout*