Prop at the top?

Propositions as types never troubled me: a proposition is a type, a proof a term of it, the Curry-Howard correspondence. In Agda, a total language, it is the whole point; in Haskell it is more slogan than tool, scary to newcomers and pointless to practitioners, since the language is partial and undefined proves anything. The nimbus around it never reaches the subtle part: Lean’s separate sort Prop…