A first draft of the SuperTask design document is now ready for review at
Comments should probably go in the GitHub PR I'm about to create or on this issue page, but the rendered version is almost certainly easier to read.
Compared to our original outline, the big change is the absence of the "Worked Examples" section. I started that, but gave up when it became clear that a lot more of the butler-side design work would need to be fleshed out. Doing that in a hurry for this document while trying to do it properly in parallel for Butler WG seemed like a poor use of time. I don't think there's anything fundamental in that; this is a case where there are many possible ways to do it and we need to carefully weigh and develop them, rather than a case where the challenge is finding any way to make it work.