The codegen plugin is in an experimental stage, quite possible some features are missing. We would need a smaller reproducing example to start fixing this.
However, something that I wanted to do as well (but so far fell short on time ), is to release an sttp+openapi integration layer, starting by generating the request descriptions using OpenAPI-codegen. It doesn’t give you tapir endpoint descriptions, but you get sttp client request descriptions - not sure if that will be enough for your use-case?