handleSessionCallback's relative redirects resolve against the backend's own origin, which 404s in this project's own supported split-origin local dev setup (frontend on Vite, backend on geniusrund, bridged by CORS). Adds GENIUSRUN_FRONTEND_URL, defaulting to PublicBaseURL for the common single-origin production case, as the fix. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>