ConfirmPayment() previously ignored PayOrderAsync return value and
always showed success screen, even when payment API returned 500.
This caused users to unknowingly create duplicate orders — one unpaid
(Validated) and one paid (Completed).
Root causes fixed:
- Pass amountTendered to PayOrderWithDetailsAsync (required by
PayOrderCommandValidator for cash payments)
- Check payment API response before showing success screen
- Show error message with retry option when payment fails
- Add loading state to prevent double-clicks during processing
Affects: CafeDesktop, CafeMobile, CafeTablet, RestaurantDesktop
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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