I'll take that money! I'll pm you my address so you can mail me a check.
Ride home was fine, everything all better, overtightened headset was definitely the culprit.
The headset was from a previous bike, so it's pretty old; it was probably "indexed" in the forward position, and when I pressed it onto this bike, by chance that "index" was slightly towards the left. Not until I recently lowered my stem and overtightened did it manifest, and now that I backed it off, it seems fine.