A partial edit, where omitting a field and nulling it differ.
Only the keys actually present in the request body are written, so sending preheader: null clears the preview line while leaving the key out keeps whatever is on file.
Successful Response
Where a digest sits between editable and shipped.
SENDING exists so the claim on a send can be taken before Resend is called: the broadcast is the irreversible step, and a status that only changed after it returned would let a double click or a retry mail every customer twice.