A cnon: nonce and its SCA verification token are consumed by a definitive charge failure (e.g. declined card) and can never succeed again, but TipPayment, UserBookingModal, UserPaymentModal and the account-page Buy-a-Gift-Card cached them and resubmitted the dead nonce on every retry — a non-retryable failure loop. The nonce/verification-token/amount/timestamp cache is now cleared in each error branch so retries re-tokenize fresh, while the idempotency key is kept for network-timeout dedup.
Fix the P0 infinite refetch in BookingFlow (payment-methods fetched once via a guard flag, was looping on empty saved-card arrays and DoS-ing the rate limiter). Extract the shared TipPayment component so tip and pay-tip routes no longer drift; reconcile formatTimeRange override_duration_minutes and subtotal/tipsPaid. CardBrandIcon gains the correct Square enum keys (DISCOVER_DINERS, CHINA_UNIONPAY). PaymentModal reads card_last4. Login links resolve to the new /terms and /privacy-policy routes. Add frontend/.env.example.