Use when deep links into an SPA/SSR page lose query params or land on the wrong screen — Next.js router.query empty on first render, redirects firing before router.isReady, login bounces dropping the intended destination, or deep-linkable pages lacking direct-navigation tests. Router/param-readiness scope; for server/client DOM divergence ("Hydration failed" / "text content did not match") see ssr-hydration-mismatch.
