After the initial assumption that my weak wrist would mean I couldn't play barre chords, I am very happy to be wrong, wrong, wrong.
I'm posting the details of what I discovered for myself in case they help others.
The thing that makes barre chords work for me in spite of my weak wrist is to set my other fingers down first before the barre -- the opposite of the "right" way, I suppose. Changing the sequence of how fingers are set onto the fret seems to change how the muscles flex and interact with each other and puts less strain on my wrist.
The other alteration that made a huge difference for me was NOT trying to twist my index finger so that the boney part was on the fret -- that alone was a big ouchy ouchy. Instead, I'm keeping the index finger straight with the fleshy part on the fret and instead of twisting it, sliding it further forward on the fret, so that the bottom edge of the fret rests against the very bottom of my finger where it meets the hand, and the tip of the index finger is hanging over the top edge unused. Scooting the index finger offsets the loss of the "boney part" advantage and adds the strength of the whole hand/arm to the mix.
[br]Having figured these two small adjustments out, barre chords slid into place pretty quickly. Tone is good, though not perfect, but all six strings are more or less ringing out, and it's easy and quick to reach for. I'm back in the game.
Thank you, all, for your suggestions -- it was playing around with them that led me to these adjustments, and next time I bitch and whine about not being able to do something, feel free to remind me of how wrong I was, LOL.
"You can get what you want or you can just get old." Billy Joel