For both the store and fetch packages...
Verify that the types are properly used everywhere.
Find a way to create a typescript component using the annotations (@wire), to avoid having to use a trick with a JS class.
Moreover, is there a way to create a membrane that works with components, without having to create a fake component?
The FetchClient results can be stored in the global store for caching, sharing and SSR purposes.
Connect to an authenticated service and add the proper headers on the fly.