Found the Problem!
Jacked up the wheels one at a time. First three were reluctant to move, but after a few rotations all spun easily. Did the left front last. Very little movement initially. I worked it back and forth until I heard something break free. Looked, and found the friction pad had snapped off the rest of the brake pad and was stuck to the rotor. I'd post images but I haven't figured out yet how to do that on here. Fascinating that the adhesive between the friction pad and the rest of the brake pad gave way before the rust-adhesion to the rotor. Definitely the first time I've seen that.
