> Ideally I'd like to be able to write types in typescript, and write python types, then verify that the types are compatible (not identical)

Have a look at https://fastapi.tiangolo.com/

FastAPI allows you to define your types in Python using Pydantic for stronger type guarantees. FastAPI also generates an OpenAPI.json file for your backend and then you can feed this OpenAPI.json document into https://github.com/OpenAPITools/openapi-generator to generate a typescript library that contains all the types. Then you don't need to verify your types, because the typescript types will be directly generated from your Python types. The generated typescript library also contains methods for each of your REST endpoints, so that you don't have to think about network requests.