Claim an unlock after paying (public)

Two shapes. { sessionId } is the instant post-checkout claim: the Payment Link redirect carries {CHECKOUT_SESSION_ID}, and a paid session returns { status: "granted", key } , store that key. { status: "pending" } means a slow payment method is still clearing; { status: "expired" } means the session is older than the 24h claim window, so use the email path instead. { email } is the restore path: it ALWAYS answers { sent: true }, whether or not that address bought anything, so never surface "no purchase found". A 429 means try again shortly , it is NOT "not purchased".