{ lib, ... }:
{
  # Common Nix daemon settings. Host-specific overrides (binary cache substituters,
  # gc retention) live in the host's default.nix.
  nix = {
    optimise.automatic = true;

    gc = {
      automatic = true;
      dates = "weekly";
      # Default retention: override per-host via lib.mkForce if different.
      options = lib.mkDefault "--delete-older-than 30d";
    };

    settings = {
      experimental-features = [
        "nix-command"
        "flakes"
      ];
    };
  };
}