pass nix binary explicitly rather than thru PATH

panel/default.nix

@@ -8,6 +8,7 @@
   },
 }:
 let
+  inherit (pkgs) lib;
   manage = pkgs.writeScriptBin "manage" ''
     exec ${pkgs.lib.getExe pkgs.python3} ${toString ./src/manage.py} $@
   '';
@@ -22,7 +23,7 @@ in
     env = {
       NPINS_DIRECTORY = toString ../npins;
       # explicitly use nix, as e.g. lix does not have configurable-impure-env
-      NIX_DIR = pkgs.nix;
+      NIX_BIN = lib.getExe pkgs.nix;
       REPO_DIR = toString ../.;
       CREDENTIALS_DIRECTORY = builtins.toString ./.credentials;
       DATABASE_URL = "sqlite:///${toString ./src}/db.sqlite3";

panel/src/panel/settings.py

@@ -193,7 +193,7 @@ if user_settings_file is not None:
 #     Replacing the `USER_SETTINGS_FILE` mechanism following the comment there would probably be a good thing.
 
 # a dir of nix supporting experimental feature `configurable-impure-env`.
-nix_bin_dir=f"{env['NIX_DIR']}/bin/"
+nix_bin=env['NIX_BIN']
 # path of the root flake to trigger nixops from, see #94.
 # to deploy this should be specified, for dev just use a relative path.
 repo_dir = env["REPO_DIR"]

panel/src/panel/views.py

@@ -58,12 +58,11 @@ class ConfigurationForm(LoginRequiredMixin, FormView):
             # serialize back and forth now we still need to manually inject the dummy user
             deployment = json.dumps(dummy_user | json.loads(submission))
             env = {
-                "PATH": settings.nix_bin_dir,
                 # pass in form info to our deployment
                 "DEPLOYMENT": deployment,
             }
             cmd = [
-                "nix",
+                settings.nix_bin,
                 "develop",
                 # workaround to pass in info to nixops4 thru env vars, tho impure :(
                 "--extra-experimental-features",