-- Owner-scoped checkout idempotency needs a stable comparison even when the
-- caller has already cleared their cart between requests. The full request
-- hash covers the cart snapshot, which differs on an empty cart; the header
-- hash is the same input minus the cart so a legitimate replay (cart cleared)
-- still matches while a different currency/address/group intent is rejected
-- as 409. Existing rows default to an empty header hash and continue to
-- allow legacy replay until upgraded.

ALTER TABLE checkout_requests
    ADD COLUMN header_hash TEXT NOT NULL DEFAULT '';