Non-blocking warnings computed at issuance for recommended-but-missing certificate fields
(vial expiration, rabies tag, DVM signature, license number). Surfaced to the UI so staff can
backfill; the certificate still issues. Empty when nothing is missing or on read-back.
isStaleboolean
True when the underlying vaccination record was edited AFTER this certificate froze its
snapshot (ITE-281) — the printed values may no longer match the record. Prompt a reissue;
never reissue silently. Computed on read for the current-certificate endpoint only.