- Add OPTIONS /api/volumen/* for CORS preflight (S-22).
- Invalidate session in require_login! when user no longer exists (S-8).
- Add check_csrf! to POST /admin/preview (S-1).
- Use File.realpath for symlink-safe containment in media_file (S-2).
- Memoize Users#all with mtime-based invalidation (S-12).
- Document that empty permitted_hosts means allow-all (S-5).
- Warn and fall back to random when session_key is too short (S-20).
petrbalvin