A very comprehensive answer, thanks :)

" ... if I was writing some kind of specialized, CRT-free code..."

One can go drama wise and ask: "Why would anyone use CRT inside WIn32
Apps?" ... It might be easy to imagine a set of macros using the Win32
and replacing the CRT code on the outside. Completely.

ps: There is also this interesting development (loosely related):

memccpy

https://developers.redhat.com/blog/2019/08/12/efficient-string-copying-and-concatenation-in-c

I am not a particular fan of "Annex K", but it seems Renie Urban
has a rather elaborate implementation:

https://github.com/rurban/safeclib

I might dare to think it seems you perhaps did not know about it at the 
time of writing :)

And. Interestingly WIN32 provides, WIN32 replacement for all CRT string 
manipulation:
(although in some kind of "crazy camel" functions naming style)

https://docs.microsoft.com/en-us/windows/win32/api/strsafe/