Can't go from model to builder when model is a MixedExperiment

[glass-ships]

One can go from the builder to the interactive model, and back again.
However, it seems like the builder will not load when coming straight from a scripted model.

Presumably because it doesn't know how to handle a MixedExperiment type?

Will likely at least require the acceptance of, and rendering a UI element for, the ratio between layers, to start with.