more generaly

modules/home/all/buildMachines/default.nix

@@ -4,5 +4,10 @@
     package = lib.mkDefault pkgs.nix;
     enable = true;
     distributedBuilds = true;
+    extraOptions = ''
+      # Let remote builders download from cache directly.
+      # This is to avoid download-cum-copy on main builder.
+      builders-use-substitutes = true
+    '';
   };
 }