Use as many "base" schemas (namespaces) as needed, and only one `api` schema which has only views & functions you want to expose.

I take this further by having an `api` schema per major version (e.g. `api_v2`). The downside is it becomes impossible to maintain more than 2 major versions at once, so you have to get everyone from v1->v2 before you can make much progress on v3, but the upside is that you should really try to avoid hard breaking changes in the DB very often.

This won't answer this question in full but perhaps some part of it.

Projects like PostgREST (and PostGraphile) use schema introspection to generate the API. When the schema changes it's automatically reflected in the API. Sure one has to keep the changes synced on the frontend but the premise is you don't want to decouple.