FluxMarket: High-Frequency Settlement Aggregator

Design a non-custodial settlement engine that aggregates liquidity from 20 different blockchains and 50 centralized exchanges. The system must guarantee atomic 'all-or-nothing' execution for complex multi-leg trades across different protocols with varying finality times. It must handle 500,000 transactions per second during market volatility and provide an idempotent API to prevent double-spending or duplicate orders in the event of network retries.