Schema UI and references
Describe forms as data that clients can render safely.
AlphaProperty schemas describe typed fields, groups, lists, layout intent and validation. They do not transfer WPF controls into Core or another client.
Use static choices for fixed values and declared option providers for resources resolved by Core. Keep option work bounded and cancellable, and bind it to the intended project/settings state.
Use PropertySchema.Reference for a literal that must identify a declared entity, with the minimum Host API for that feature. Editable suggestions are not automatically entity references; runtime templates are checked in their own context.
Mark protected fields appropriately. Never place a current password/token in a default value, help text or preview.
Detached parent/entity schema callbacks must not mutate live state. See Entities.