Derailleur and clearance
The rear derailleur is very tight, even with the extra hangar extender. The in progress photo without it was when I realized it wasn't going to clear.
Maybe that is the problem. I think I may have a little more B-screw margin.
Or, maybe move the wheel further back in the dropouts. My reading suggested that would increase clearance, but experimenting (before the hangar extender) didn't seem to really help.
At the current position, I could definitely take out one chain link pair. That would keep the derailleur more extended. I didn't do so because it's a more destructive adjustment, and because I wasn't sure if the wheel was where I wanted it.
I'll do pads, adjust B screw, do H,L barrel of rear derailleur, and try again. If it's glitchy I'll try to watch while riding, as suggested.
Thank you to all for the comments!