router.update.channel names the nixpkgs branch to follow (unstable or a release like 26.05). router-upgrade check compares its newest tested revision with the running one; preview locks a copy of the configuration flake to it and lists the packages that change version and the size of the download without fetching anything; download fetches it; apply takes the lock and activates with commit-confirm, the lock going back on a rollback or a failed build. router-update keeps an upgraded nixpkgs pinned. Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01AeFqV9dZrK6nipHkPfyM4F