try and fix deployment

flake.nix

@@ -7,6 +7,8 @@
     mtce.inputs.nixpkgs.follows = "nixpkgs";
     microvm.url = "github:microvm-nix/microvm.nix";
     microvm.inputs.nixpkgs.follows = "nixpkgs";
+    deploy-label.url = "path:./misc/deploy-label";
+    deploy-label.flake = false;
   };
 
   outputs =
@@ -15,6 +17,7 @@
       nixpkgs,
       mtce,
       microvm,
+      deploy-label,
       ...
     }:
     let
@@ -23,6 +26,12 @@
       pkgs = import nixpkgs { inherit system; };
 
       flakeRev = self.shortRev or self.dirtyShortRev or "unknown";
+      deployLabel =
+        let
+          labelFile = "${deploy-label}/label";
+          raw = lib.removeSuffix "\n" (builtins.readFile labelFile);
+        in
+        if raw != "" then raw else null;
 
       customPkgs = {
         hopper-rs = pkgs.callPackage ./packages/hopper-rs.nix { };
@@ -56,7 +65,7 @@
 
       specialArgsFor = hostName: {
         hostInfo = hostInfoFor hostName;
-        inherit inputs customPkgs flakeRev;
+        inherit inputs customPkgs flakeRev deployLabel;
       };
 
       hostDefFor =