Use named parameter syntax in Vercel rewrite and add <base href="/"> tag to ensure assets load correctly from root when serving index.html through the API.
Instead of redirecting, serve the static index.html file directly. The Vercel rewrite preserves the /a/{naddr} URL, allowing client-side SPA routing to work correctly.
Browsers get 302 redirect to / where the SPA handles routing client-side with the original /a/{naddr} URL preserved. Crawlers/bots get the full HTML with OG meta tags.