Set YTDLP_COOKIES_HOST in server/.env and compose mounts the host cookies.txt read-only at /cookies.txt and wires YTDLP_COOKIES automatically — no compose edits per host. Falls back to /dev/null when unset so the container still starts. Add server/.env.example, gitignore server/.env, and document the flow. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>