More recent revision: https://isocpp.org/files/papers/P2900R10.pdf. It seems like they've added a few things since this draft.
It's somewhat funny to hear "minimum viable product" in the context of a language standard/specification. I'd never thought of adding a feature to a language in that way before.
The idea of design by contract (DbC) in C++ appears to have been around for a while too. The authors link to a "forthcoming companion paper" (currently a 404 error), but you can find proposals from as early as 2004 with the idea: https://www.open-std.org/JTC1/SC22/WG21/docs/papers/2004/n16...
(and potentially earlier, I just haven't seen one yet)