#data loss

1. 📌 Tighten validation: only allow StaticPropSource in XB fields + PageTemplate, DynamicPropSource in ContentTypeTemplate Active started forbidding DynamicPropSources from being used in XB fields (i.e. in a specific content entity's XB component tree).
2. I'm working with @lauriii to refine the plan for 🌱 [META] 7. Content type templates — aka "default layouts" — clarify the tree+props data model Active . The direction that is going, it looks like the tightened validation we introduced in #3481720 will become permanent.

That means that the issue title/scope here is wrongContentTypeTemplate will simply have to reflect every DynamicPropSource in its component tree as an explicit config dependency.

If we do that, then Drupal's config dependency system takes care of this problem for us! We should still confirm it with explicit test coverage though, and that's what this issue is about.

IOW: 📌 [PoC] Introduce a `ContentTypeTemplate` config entity Active should have introduced the necessary config dependencies already, and it should be up to this issue to add explicit test coverage for it.