Add reproducible Nix dev environment

Replace the Python venv with a Nix devshell pinning ansible-core 2.21.3,
ansible-lint, yamllint and a Python with proxmoxer/requests. The Python
dependencies share the interpreter that runs ansible, so pve-*.yml plays
on implicit localhost can import proxmoxer without inventory changes.

The shellHook exports absolute ANSIBLE_CONFIG, ANSIBLE_INVENTORY,
ANSIBLE_ROLES_PATH and ANSIBLE_COLLECTIONS_PATH, so commands work from
the repository root as well as from ansible/.

Also un-ignore .envrc, which the global gitignore hides, and ignore the
stray .ansible/ runtime directory.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GTocXkGUUazHdKKd3r9k71

.envrc

@@ -0,0 +1,3 @@
+# direnv: load the Nix dev shell defined in flake.nix
+# Enable once per checkout with: direnv allow
+use flake

.gitignore

@@ -20,3 +20,9 @@ __pycache__/
 .direnv/
 result
 result-*
+
+# direnv shell hook lives in the repo (global gitignore hides it)
+!.envrc
+
+# Ansible local runtime dir (facts cache, locks)
+.ansible/

flake.lock

@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1787498568,
+        "narHash": "sha256-9i/VTdusq/+NM/tz+J1Re+ojkMB8MBf0QshnYfzHz30=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "56c02bc00adcf003215cc4bd996d6efaf4cff188",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,87 @@
+{
+  description = "HomeLab infras — reproducible Ansible control-plane dev shell";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  };
+
+  outputs = { self, nixpkgs }:
+    let
+      systems = [ "x86_64-linux" "aarch64-linux" ];
+      forAllSystems = f:
+        nixpkgs.lib.genAttrs systems (system: f nixpkgs.legacyPackages.${system});
+    in
+    {
+      devShells = forAllSystems (pkgs:
+        let
+          # One Python environment carrying ansible-core *and* the libraries the
+          # modules import in-process (community.proxmox needs proxmoxer +
+          # requests). Ansible sets ansible_python_interpreter for the implicit
+          # localhost to sys.executable, so `hosts: localhost` and
+          # `delegate_to: localhost` tasks pick these up automatically.
+          pythonEnv = pkgs.python3.withPackages (ps: with ps; [
+            ansible-core
+            proxmoxer
+            requests
+          ]);
+        in
+        {
+          default = pkgs.mkShell {
+            name = "homelab-infras";
+
+            packages = [
+              pythonEnv
+              pkgs.ansible-lint
+              pkgs.yamllint
+              pkgs.git
+              pkgs.jq
+              pkgs.openssh
+              pkgs.curl
+              pkgs.gnumake
+            ];
+
+            shellHook = ''
+              repo_root="$(${pkgs.git}/bin/git rev-parse --show-toplevel 2>/dev/null || pwd)"
+              ansible_dir="$repo_root/ansible"
+
+              if [ -f "$ansible_dir/ansible.cfg" ]; then
+                # ansible.cfg spells its paths relative to ansible/, so pin them
+                # absolutely here — that makes the shell usable from the repo
+                # root as well as from inside ansible/.
+                export ANSIBLE_CONFIG="$ansible_dir/ansible.cfg"
+                export ANSIBLE_INVENTORY="$ansible_dir/inventory/hosts.yml"
+                export ANSIBLE_ROLES_PATH="$ansible_dir/roles"
+                export ANSIBLE_COLLECTIONS_PATH="$ansible_dir/collections"
+              else
+                echo "warn: $ansible_dir/ansible.cfg not found — run commands from ansible/" >&2
+              fi
+
+              # Banner goes to stderr so `nix develop --command ...` keeps a
+              # clean stdout for scripting.
+              {
+                _ver_ansible="$(ansible --version 2>/dev/null | head -n1 | tr -d '[]' | awk '{print $3}')"
+                _ver_lint="$(NO_COLOR=1 ansible-lint --version 2>/dev/null | tail -n1 | awk '{print $2}')"
+                _ver_yaml="$(yamllint --version 2>/dev/null | awk '{print $2}')"
+                _ver_py="$(python3 --version 2>&1 | awk '{print $2}')"
+
+                echo "HomeLab infras dev shell"
+                echo "  ansible-core  $_ver_ansible"
+                echo "  ansible-lint  $_ver_lint"
+                echo "  yamllint      $_ver_yaml"
+                echo "  python        $_ver_py (proxmoxer, requests)"
+                echo ""
+                echo "ANSIBLE_CONFIG=$ANSIBLE_CONFIG"
+                echo ""
+                echo "Galaxy collections are NOT installed automatically. Run once:"
+                echo "  ansible-galaxy collection install -r $ansible_dir/requirements.yml -p $ansible_dir/collections"
+                echo ""
+
+                unset _ver_ansible _ver_lint _ver_yaml _ver_py
+              } >&2
+            '';
+          };
+        });
+
+      formatter = forAllSystems (pkgs: pkgs.nixpkgs-fmt);
+    };
+}