> Does seem to take a lot of work to redefine all the types from the existing services (unless I'm missing something).
The goal is to keep this type of rework minimal-to-none, by leveraging the type data that's already there. In typed languages, if the contracts are well typed, then you're already 90% of the way there.
> Given a rest service output, can't some of these things be auto generated ?
Exactly. For example, Vyne can work with a plain old swagger file, which many services already have. From there, it's a little additional metadata to identify ID's etc.
However, the idea is that getting Vyne working should be much less code than the alternative - which is to write the integration code manually. Also, getting Vyne going is a one-off cost, which should remain robust as the surrounding services change their APIs.