Turbopack was not dead-code-eliminating the typeof window ternary correctly, causing the server-side fallback (http://localhost:3000) to leak into the client bundle. The browser then made cross-origin requests to localhost instead of same-origin relative URLs, producing "NetworkError when attempting to fetch resource" on staging. Replace the fragile process.env pattern with a simple literal: client always uses '' (relative URLs via Caddy), server uses API_INTERNAL_URL.