add lan store url option as cli flag

README

@@ -1,3 +1,8 @@
+On build device:
+* nix-build
+* (for LAN builds) nix-build --arg mlabs true
+
+On target device:
 * Enter BIOS, disable secure boot, enable UEFI PXE network boot
 * sudo auto-install
 * sudo reboot

default.nix

@@ -43,20 +43,26 @@ let
     nixos-install --no-root-password --flake /mnt/etc/nixos#artiq
     ''; 
 
-  customModule = {
+  customModule = mlabs:
+    let storeUrl = "https://nixbld.m-labs.hk" + (if mlabs then "?priority=10" else "");
+    in
+      {
         system.stateVersion = "24.05";
         environment.systemPackages = [ autoInstall pkgs.git ];
         documentation.info.enable = false; # https://github.com/NixOS/nixpkgs/issues/124215
         documentation.man.enable = false;
         nix.settings.trusted-public-keys = ["nixbld.m-labs.hk-1:5aSRVA5b320xbNvu30tqxVPXpld73bhtOeH6uAjRyHc="];
-    nix.settings.substituters = ["https://nixbld.m-labs.hk"];
+        nix.settings.substituters = [ storeUrl ];
       };
 
+in
+  { mlabs ? false }:
+    let module = customModule mlabs;
     in
       makeNetboot {
         modules = [
           <nixpkgs/nixos/modules/installer/netboot/netboot-minimal.nix>
-      customModule
+          module
         ];
         system = "x86_64-linux";
       }