The backend in some places assumes the shape of Z4s and Z3s (in validation, or copying objects). The frontend has bespoke displays and editing interfaces for some types. This task is to ensure that the identity property on keys can be set through the interface.
This does not include making the type interface easily usable. We still assume that only staff edits the structure of types for now (this will be changed in a later task).
For now, Identity fields on custom types can only be Z9/References to the containing object.