I am an idiot.
I made a mess of this one pot during the dinner-making process (who knew that onions & mustard seeds1 cannot saute themselves while one takes a brief shower?), and so I was employing some major elbow grease to free the burned blackness from the bottom. I paused to read up on the grease-fighting properties of my cleaning liquid, at which point I realized I was washing the dishes with hand soap.
And I have been for at least a week. At some point, I pulled the hand soap from underneath the cabinet instead of the dish detergent, and, since I never got around to putting it away at least this week, I’ve been washing all of my dishes that don’t go in the dishwasher with hand soap.
1 In case anyone’s curious, I was using my awesome new cookbook to make (an enormous batch of) Chickpea-Spinach-Curry.