I have the multi-artifact-grid example working and discovered that I could only get it to work by leaving the stubbed CustomApp that rab init created. By that, I mean that I had to leave that first stanza in there that declared 'CustomApp'. Beyond that is the code I pasted in from the multi-type-grid example code (with a few tweaks).
Both the CustomApp and the BOA.AdoptedWord.MultiArtifactGrid extend Rall.app.App. I thought there could only be one Rally.app.App "in" an App, or to serve as "the" app. What does it mean to have all of these Apps within one app?