At first, I thought the ice maker had gone bad. But then realized the frig side was getting warmer, so it was something bigger than just the ice maker.
After doing some searching, i found this video, which was incredibly helpful.
https://www.youtube.com/watch?v=EF14XHW9jWw
In particular, the tip about checking continuity through the two connectors. The results sent me directly to the freezer's Defrost Thermostat and the Defrost Heater. Both were dead; the defrost bar glass was totally black, from the coil having shorted.
Took an hour with a hair dryer to get rid of the frost buildup. Let the unit sit for a day while waiting for the parts to arrive. Installed the thermostat and defrost heater in less than an hour. Because the defrost heater had shorted, I cut the female shielded connectors from the ends of the two wires, crimped on new ones, and connected. For the thermostat, I used simple butt splice connectors.