Your question is Real-Time Inventory Service. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Design a real-time inventory and stock-status service that powers product pages on a large e-commerce site for Walmart Labs, with warehouse updates within seconds and holiday-scale read traffic; reflect caching strategy, fallback when a regional store is unavailable, and how you would resolve write conflicts across distribution centers.