So...yeah:
Based on my receipts these were chain autoparts store pieces (lifetime warranty lol).
As much as this thing sits, and as bad as the condensation can be, maybe this is to be expected? For the last three years it's been sitting for probably 1053 of the total 1095 days. My suspicion is this is more likely just cheap, garbage pads, but I do wonder if maybe they were wet, somehow absorbed water, then froze? To me that seems the most likely cause based on the way they are breaking apart yet still (except the one) generally intact. It was definitely cold (for here, low 20's) the first few days I was using the thing, maybe that was it.
No damage to the rotors, and I'm guessing the squeaking I heard was the left side pad separating.
I couldn't turn the right side tire/wheel, so had to beat that caliper free from it's mount. As I stated in the beginning, the brakes have pulled left for quite a while. The mounting pins on the right side had very small shiny spots, so I don't think it was moving much. I was able to compress the piston into the bore as easily as the left side, and if the pictures aren't clear, the pads were still plenty thick.
Got new pads, new hardware, and a caliper "rebuild kit" (the two seals) coming. I'm not going to do the caliper seals until/unless I can figure out the caliper is definitely the issue, but I won't take it off the jackstands until I've bled them thoroughly (again) and tried to make sure they are working evenly, as best I can before test driving. With so few miles I don't think the pads would have worn enough to show a bias to one side.