Design an Uber Eats Cart Service

Design the shopping cart service for a food delivery platform similar to Uber Eats. The service should allow customers to add, update, and remove menu items from a cart before checkout. A cart is associated with one customer and typically one merchant or restaurant. The design should cover: - Core user flows: create cart, add item, update quantity, remove item, view cart, and submit cart to checkout. - Handling menu item options, modifiers, prices, taxes, fees, promotions, and availability. - Data model and APIs. - Consistency requirements between cart, menu, pricing, inventory or availability, and checkout. - Scalability, reliability, and failure handling. - Edge cases such as restaurant closing, price changes, unavailable items, multiple devices, and abandoned carts.