> Even the languages that sorta kinda support this, don't, really. They encode specific bits of functionality vaguely inspired by monadic handling, but out of the Haskell family of languages I don't think I've yet seen a full, true implementation of "monad" in general that anyone uses.

I just updated the links to FP-TS and Sanctuary... have you checked those out? They seem to tick all the boxes as far as I can tell.