A team relies on StrictMode's render-phase double-invocation to catch impure components. Their component reads `performance.now()` during render to derive a value and they expect the two dev renders to differ and flag the impurity, but React shows no warning and the component 'passes'. Why does StrictMode NOT automatically detect this kind of impurity?
function Clock() {
const t = performance.now(); // read during render
return <span>{t}</span>;
}