Well, I must say I don't see how tonight could have gone in a more congenial manner on this front.
It started off same as before, even with Shadow hissing at me when I first walked in the door. He was still hiding behind the blinds, so maybe he didn't get a good look at me. I was distressed to see he had not eaten nor taken water, nor even relieved himself anywhere I could find. I let me concern get the better of me slightly, and put some water in a frying pan and set that over in his claimed area of the living room.
He didn't drink, but after I sat down in a chair across the room and stayed there for 5 or 10 minutes, he relocated to the arm of the couch, and sat there yawning for another 10 minutes. Then he moved on top of one of the boxes I'd set for him, and sat there yawning for a bit longer. Then he jumped down on the floor and started meowing at me repeatedly.
I lowered a hand down to his eye level near my chair and beckoned him vocally, and he came over and let me stroke him, then walked away, sat down... and meowed again.. then came back. I stroked him a few more times and thought to remind him of where his amenities were located - first placing him in the litterbox.
He left the litterbox as soon as I sat back down, and went back over to his boxes. I moved to my end of the couch. He started meowing again, I "replied," and he came back over and let me pick him up again. This time I showed him his food and water again, and returned to the couch. He ate one or two nibbles, then moved back to me. I used the feathery dingle-bopper thing on the top of the scratching post to entice him, and he seemed to enjoy scratching very much. After a few seconds of that, he went back to the food and ate quite a bit. Then wandered around exploring (with me staying on the couch in his sight so as not to startle him back into hunkering down), and then he went to the litterbox. And I tell you it was like that scene in "A League of Their Own" where Tom Hanks just pisses... and pisses... and pisses... and pisses. Holy cow. I didn't think a cat could hold so much liquid.
Anyway, after that he was feeling much better apparently, because he came up on the couch with me and let me stroke and scratch him for a while, and purring.
So. I'd say that's pretty good progress.