CEL came on, checked with a bluetooth ODB reader from Amazon, read P1457. Googled and found likely culprit was EVAP solenoid, watched a ten-minute Youtube video on replacing it, video maker had amusing parrot. Got under car and removed canister with impact driver and if I remember correctly a 12mm socket, found solenoid to be badly corroded. Was able to remove one screw with vise grips, totally unable to do anything with other side. Attempted penetrating oil, vise grips, cutting a slot and using a flat head screwdriver, then cutting an X and using a Phillips, then cutting flats for vise grips. Ended up just dremeling it off. Replaced solenoid, applied some silicone grease to O-ring and reinstalled canister, total cost ~$40 with one-day shipping, just in time for new inspection sticker.
Apparently it was the EVAP Control Canister Vent Shut Valve Solenoid. The dealership would not honor the service with a "good faith repair" (big surprise there). But now I have acceleration issues following the service and have not yet had that resolved.