The interesting problem in arbitrage is not finding the price difference: it is what to do when only one leg fills. The prototype treats that as the normal case, not the exception.
The leg state machine handles partial fills and rejects, and offers four policies when a leg does not go in: wait, cancel the other, hedge, or unwind. On top of it run per-issuer limits with an uncovered alert, P&L and a kill switch. Underneath, an append-only journal where every decision is written before it is acted on.
What it is not: there is no real market feed, no FIX, no orders. It runs on a replay of five recorded days or on delayed public data, and execution is simulated. We promise no latency figure until it is measured against a real feed.