Create a way to have a top-level project

As the API stands, a project seem to correspond to different parts of a construction project: project A is the west wing of the building, project B is the east wing. Or a railway would be split into stations, rail sections, etc.

There is a problem when we have users intervening for multiple clients. For instance, a superviser could work for both a school for client A and a railway for client B. Both clients could have split their work into several hundreds (or even thousands) "projects". How would that work out for the user? Either they see all projects of all clients they work with, and in that case, there is not enough information in the returned data to filter (just a name and ID ???). Or there could have some parameter to filter the projects for a client.