Developing applications and libraries at the same time should be easier

Background

Switching from a library workspace to an application workspace after making changes to the library is cumbersome. For example, say I want to make some changes in library L and test them in application A. Opening a build shell for library L does not really work, since a full bst build L.bst is required to get an updated version of library L into application A's shell. So my current workflow is to bst build L.bst outside any shell, then enter a A.bst shell to test my changes. Let's say I'm debugging an issue by adding printfs to the library. That means I have to build, enter the shell, find any problems with my change (it's not enough, I need another printf!), exit the shell, build again, reenter the shell... and entering and exiting shells takes a nontrivial amount of time. It's simply harder to do serious library development with BuildStream than it is without.

I don't know what we could do about this. I guess one option would be to allow building multiple elements in a single shell, so e.g. I could hack on WebKit (library L) without leaving my Epiphany (application A) shell.

Task description

Not sure

Acceptance Criteria

Not sure.