Hooks

React uses reference equality, not value equality, to detect dependency changes — how that low-level semantic turns a harmless empty-array fallback into an infinite setState loop, and why the same code is merely wasteful on the web but fatal on mobile.

Reframing "calling a hook in an async function always crashes" as a render-time contract problem, "the giant configurable component" as a composition-vs-configuration tradeoff, and accessibility as a testing contract.