Recomputes the field definitions after a client-side change to one or more fields. Send the current fields payload as the request body — typically after a field marked requiresUpdate: true was edited — and the response returns the same shape with derived and dependent fields refreshed and any custom-field scripts re-evaluated. Unlike the GET variant, no fields are seeded from server-side records; the client's payload is the source of truth. Pass applyScanResult=<contentId> to fold receipt-scan results into the response.