Что сказать
«Layouts — shared shells wrap segment и below, compose root down. Persist across navigation — sibling pages, only innermost page re-renders, enclosing layouts mounted — state, scroll kept — app-like navigation. Corollary: wrong place per-route data — don't re-run between children — classic stale bug. Reset per navigation — enter animation, fresh error boundary — template not layout. Route groups parentheses — layout subset или organise files без URL segment.»
Итог
Layout pitch: persist = UX win, stale data = architectural mistake.
Next.js · middle · сложность 5