The project-rollup forms derive originator from the selected Package
(party folder) server-side, so the field is read-only and was blank
until submit. Add a declarative `ui:mirrorFrom: <sibling>` hint: the
object renderer wires the named sibling's input to the field so the
read-only originator updates live as the user picks a party — the
composing tracking number is visible while filling the form. Display
only; the server stays authoritative via the cascade's folder_fields.
Set `ui:mirrorFrom: party` on originator in the embedded
default-project-{mdl,rsk}.form.yaml. Generic hint, not hardcoded field
names, so operators can reuse it.
Test: form-safety.spec.js — filling the source field updates the
read-only target; the target is not editable.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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