Well, oops. I neglected to think about chain wear on the weekend fun bike all this year, and the predictable turns out to have happened. I've definitely overdone the chain and I suspect I've cooked the rear cassette and at least one front chainring (I'm almost always on one, so the other two may have survived).

This is going to be a bit costly, but I did manage to go just over ten years without this particular accident happening. Still, this is my sad face. Next year, do better, me.