Hello Patrick! Thanks for the writeup; gradually incorporating it into my config.

BTW, I recall reading a PR you started on fixing the fallback from failing substituters? This may be of interest to you:

• https://discourse.nixos.org/t/announcing-ncps-a-nix-cache-proxy-server-for-faster-builds/58166/18
• https://github.com/NixOS/nix/pull/13301