Well, my alarm was still set to yesterday's late start schedule, so I had to jump out of bed and into clothes and leave as fast as possible.
Zoomie still squeaked, but I didn't really hear clunking at all this time, which strikes me as extremely odd. I'll have to see if it happens on the way in this afternoon, since Zoomie is now the only bike I can ride.
On the bright side, I learned how to swap shifters and their cables over from one bike to another and adjust both derailleurs passably well. I spent all morning with my husband getting a blue freebie bike that he decided he liked better set up to actually be a bike, instead of a collection of parts that looked like one. My poor green Chainless is naked... she donated shifters and cables, handlebar grips, and both wheels to the blue bike.
I'll definitely try a sideways oiling for Zoomie and see if that stops the squeak.