Settle a premium offer and apply the product

Checks the offer's invoice for settlement (LUD-21 verify at the provider) and applies the product effect EXACTLY ONCE — a replayed redeem answers applied: "already" with the account's current premium state, never a second effect. Non-refundable; time products extend from max(now, current expiry) so a second purchase stacks, and the credits product adds credits. Poll this at ~2.5 s after paying until it stops answering 202. The claim is bound to the paying account: another account's macaroon is refused, and an expired macaroon still resumes an already-paid claim. NOT gated by PREMIUM_ENABLED (a paid claim must always resolve); PAYMENTS_ENABLED off answers 503 so the poll stays alive. Rate limited 60/min/user. Every answer is private, no-store.