My tool https://openapi-code-generator.nahkies.co.nz/overview/about generates typed handlers based around koa (routing, req/res validation using zod) from openapi 3, as well as typed clients with optional zod validation using fetch/axios.
It also supports typespec using their transpilation to openapi 3 tooling
From my understanding trpc is very similar, however, the rpc mechanism is not a standard. ts-rest produces openapi schemas and speaks REST over http, as well as a typed client.
That being said, I am actually slowly migrating off ts-rest and adopting @effect/schema and @effect/platform/HttpApi, I foresee this being the direction the typescript ecosystem heads in over the next few years. However, the APIs are not stable yet and it has a bit of a learning curve, so would not adopt lightly
I really wanted to adopt tRPC but the deal breaker was it being opinionated on status codes without allowing configurability. Because I needed to meet an existing API spec, that meant ts-rest was a better option. I think there's an aditional option with a native spec generator in frameworks like Hono, and maybe Elysia.
Thinking maybe Zod + Zod open API.
Really looking to replicate similar spec first workflow similar to protobuf services.
https://typespec.io/ also looks promising but seems early.