Note 02 · systems
Economic correctness matters
A strategy can be technically correct and economically wrong. The job of an execution system is to be the second kind of correct.
Modelled spread is a number. It is not a profit. Between the model and the realized PnL sit gas, L1 data cost, flash premium, ordering cost, slippage, price impact, and an honest reserve for the things you forgot.
Phoenix models every one of those, conservatively, before the engine ever asks the executor to sign. If the conservative estimate is below the retained-profit floor, the opportunity does not exist — not even as a thought experiment.
A system that models only the upside is a system that will be surprised by the downside.