There seems to be some missing documentation for the available web API operations?
In addition to the operations listed here - http://docs.grandnode.com/web-api
I noticed there are more operations available, like for ShoppingCart - https://github.com/grandnode/grandnode/tree/develop/Grand.Web/Controllers

Are these documented somewhere else, or have i missed something?

Controllers for Web API operations are listed here: https://github.com/grandnode/grandnode/tree/develop/Grand.Web/Areas/Api/Controllers/OData

Controllers that you've sent are responsible for the whole store.