This Next.js version generates LayoutProps/PageProps/RouteContext into .next/types only via `next dev`, `next build`, or `next typegen` (see node_modules/next/dist/docs .../06-cli/next.md). Typecheck ran `tsc --noEmit` standalone before Build, so those globals didn't exist yet, failing with "Cannot find name 'LayoutProps'". Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>