me-imfhd/velocity — reverse-engineered prompt

Build me a fast crypto exchange backend called Velocity. I want users to be able to place market orders and limit orders, cancel one order or all orders, and ask for their open orders. It should support multiple markets at the same time, keep each market’s orderbook in memory for speed, match bids and asks correctly, lock and update user balances, and return order responses quickly.

Use Rust for the core service. Use ScyllaDB to persist orders, balances, trades, and enough history to recover the orderbooks if the engine restarts. Use Redis queues or pub sub where it makes sense for order responses and event flow. Add WebSocket streams for public trade, ticker, and depth updates, plus private order updates for the user who made the order.

Please include Docker setup so I can run the services locally, and add a small API collection or examples showing how to place, cancel, and inspect orders. Look up current docs online if you need to.