The biopsy's back; the Evil Kidney was cancerous. Fortunately, it was stage-1, meaning the cancer was enclosed and hadn't metastasized. Doc says there's a 5% chance I'll need to worry about that.
In the 2 weeks since the evil one was removed, all sorts of things have improved:
--My lower legs had been swollen since January, but the swelling's maybe 95% gone. That hasn't improved the walking issues, which are likely a blood-flow matter.
--My blood pressure's down to the point where I have to scale back my meds.
--I'm feeling a bit more energetic, but I still get worn out pretty quickly. Lots of sleeping and naps.
Speaking of which...
Tinkercad has a nifty Arduino simulator
23 minutes ago