The TypeScript language service which powers IDEs and which is maintained/shipped with TypeScript already has the knowledge of all the types in your application. It seems like it would be relatively straight-forward (though a lot of work!) to develop some sort of code gen library that uses the TypeScript types known to the language service to reflect on those types and emit some sort of runtime type validation functions as part of a build step. This could be done in an npm module similar to webpack or in an IDE plugin. If that functionality doesn't exist today given all the listed open source projects, I'm kind of surprised. I don't think the TypeScript team would need to do anything to allow such a project to be developed.
It has quite an awkward way of being distributed. If you google for standalone TypeScript language services you'll find unofficial ones. Deno's is much simpler. Maybe they should pioneer this.
