Alright, an update.
I took the damn thing to a bike shop, put a 12mm into a vice, and tried to turn the wheel.
First horizontally, then vertically, with two fully grown men , one of them (me) channeling my extended annoyance, at the same time while the 12mm allen key was flexing the better part of 45 degrees.
Any more pressure and the allen key might have failed spectacularly and dangerously.
So, as much as I would like to give up, I'm not.
One of my friends likely has a 12mm socket and an impact wrench.
After that, I'm thinking blowtorch.
After that, thermite.
Maybe a tactical nuclear strike.