I build and run what a trading desk is made of: market data coming in, research in the middle, orders going out. On the data side that is the exchange feed, tick distribution across equities, derivatives and commodities, a serving API, and a platform whose pipelines and quality gates research replays. In the middle it is the simulation engine an idea has to clear — next-bar fills, real Indian costs, walk-forward — and the paper stage that uses the live order path. On the execution side it is a control layer turning one master trade into orders for twenty to thirty client accounts, and an OMS layer where each instance holds every client on its broker. Python across the desk, C++ where the packet path is hot, two-plus years of it in production in Mumbai.
Everything below is drawn, because the useful question about a trading system is never the feature list — it is what the shape is, what is allowed to block an order, and what happens at 09:16 when a broker stops answering. Every stage on the drawing opens into what I actually built there.