I know exactly what you mean. Earlier versions of Dagger actually took this "embedding" approach: any CUE configuration is a valid Dagger configuration, with an extra layer of annotation that describes how to make that configuration runnable. What we learned is that this model is thoroughly confusing to almost everyone except hardcore CUE enthusiasts.

Now we use CUE in a more straightforward way: as a superior replacement for YAML. There's a (simple) schema that all Dagger plans must follow; beyond that, you can import any CUE package and apply any definition into your plan. But you don't need to go upstream and annotate these packages with additional Dagger metadata.

I'm not sure if my explanation is clear - even I get confused by this embedding business sometimes.