Why audit at all
The failure you are looking for is silent by design.
Nothing in the system announces that it is under-delivering, because every layer computes correctly from whatever it was handed. A journal missing three fields per trade still produces a weekly summary. A tier ceiling set by habit rather than by drawdown still appears in the panel. A capture-efficiency figure computed from a mistyped fill still renders. The absence of errors is therefore not evidence that the machinery is working, and the only way to establish that it is working is to check a small number of specific outputs against something outside the system. That external reference is what makes these checks worth the minutes they cost — an audit conducted entirely inside the workbook would confirm only that the workbook is internally consistent, which was never in doubt.
Each check either passes or localises the fault. The loop is worth running once in month one and once a quarter afterwards — most defects found this way are in capture, which is the operator's to fix rather than the system's.
