I added support for typespec as an input specification to my openapi 3 based code generator a couple of days ago.

They provide an API to convert to openapi documents so it was pretty painless (https://github.com/mnahkies/openapi-code-generator/pull/158)

My focus is on doing both client sdk and server stub generation, though only typescript so far - will hopefully add other languages eventually, when I'm satisfied with the completeness of the typescript templates.