Well, my laptop is back in service.
I ended up installing on another nvme drive and then dd'ing the first 6 megabytes from that drive to the original nvme.
That put back enough necessary goo that my OpenBSD label was restored. I hadn't expected that honestly. I would have figured that I might get the disklabel from the donor disk, which may or may not have been exactly the same. Then I figured I'd restore the disklabel from the backup on /var on the original disk. While investigating that idea, I discovered the disklabel showing on sd1 was different than sd0. Whee.
I _wanted_ to get the original drive booting, but it wouldn't and installboot didn't want to work (honestly, I've _never_ gotten it to work outside of the intaller).
So I copied all my files in /home over. I restored a number of config files from /etc. Then I used my backed up package list to restore the packages. I'm sure I missed a few packages and will bump into some other things.
For now though, I'm back in action.