Should builds issued via IBuildEngine from tasks fail with the "Undeclared reference" check?

There's two static graph isolation constraints:
1. all referenced projects must be declared before usage
2. there should be no cache misses

Building an undeclared project via the MSBuild task triggers constraint 1., but building a project via the IBuildEngine callback from within a task triggers 2. Should it instead fail with 1. and report which task tried to do it?

This is more of a fit and finish thing, since the build will fail either way. It's just that type 1 failures are easier to understand than type 2. IsolateProjects_Tests has some commented out `InlineData` elements which exercise this path.