Your example already exists, it’s called TSON, unless you are complaining about how they had to implement that I also disagree that type validators like Zod/io

Your example already exists, it’s called TSON, unless you are complaining about how they had to implement that I also disagree that type validators like Zod/io-ts would benefit from plugins, they are just js code in the end that does defensive checks for you. Unless you have something else in mind