Performance

It pushes server rendering or islands architecture for above-the-fold content, code splitting by route, and lazy loading everything else. The layout shift rules are practical: reserve space with aspect-ratio, size skeletons to match final content, never inject above existing elements. Animation discipline is strict, compositor-only properties with reduced motion support. The verification step actually throttles to slow 4G and 4× CPU, which will catch problems your MacBook won't. Treat this as accessibility work, because jank hits low-end devices hardest and performance budgets are really user-exclusion budgets.