fix: install nix tooling in bootstrap workflow when missing

.gitea/workflows/kubeadm-bootstrap.yml

@@ -107,13 +107,42 @@ jobs:
 
       - name: Validate nix installation
         run: |
-          if [ ! -x /nix/var/nix/profiles/default/bin/nix ]; then
-            echo "Nix not found at /nix/var/nix/profiles/default/bin/nix"
-            exit 1
+          if [ -x /nix/var/nix/profiles/default/bin/nix ]; then
+            /nix/var/nix/profiles/default/bin/nix --version
+            exit 0
           fi
 
+          if command -v nix >/dev/null 2>&1; then
+            nix --version
+            exit 0
+          fi
+
+          echo "Nix missing; installing no-daemon Nix for this runner job"
+          sh <(curl -L https://nixos.org/nix/install) --no-daemon
+
+          if [ -f "$HOME/.nix-profile/etc/profile.d/nix.sh" ]; then
+            . "$HOME/.nix-profile/etc/profile.d/nix.sh"
+          fi
+
+          nix --version
+
+      - name: Install nixos-rebuild tool
+        env:
+          NIX_CONFIG: experimental-features = nix-command flakes
+        run: |
+          if [ -f "$HOME/.nix-profile/etc/profile.d/nix.sh" ]; then
+            . "$HOME/.nix-profile/etc/profile.d/nix.sh"
+          fi
+
+          nix profile install nixpkgs#nixos-rebuild
+
       - name: Run cluster rebuild and bootstrap
         env:
-          PATH: /nix/var/nix/profiles/default/bin:${{ env.PATH }}
+          NIX_CONFIG: experimental-features = nix-command flakes
+          PATH: $HOME/.nix-profile/bin:/nix/var/nix/profiles/default/bin:${{ env.PATH }}
         run: |
+          if [ -f "$HOME/.nix-profile/etc/profile.d/nix.sh" ]; then
+            . "$HOME/.nix-profile/etc/profile.d/nix.sh"
+          fi
+
           ./nixos/kubeadm/scripts/rebuild-and-bootstrap.sh