+devshell with opencode rules

flake.nix

@@ -4,13 +4,21 @@
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
     flake-utils.url = "github:numtide/flake-utils";
+
+    m3ta-nixpkgs.url = "git+https://code.m3ta.dev/m3tam3re/nixpkgs";
+    agents = {
+      url = "git+https://code.m3ta.dev/m3tam3re/AGENTS";
+      flake = false;
+    };
   };
 
   outputs = {
     self,
     nixpkgs,
     flake-utils,
-  }:
+    m3ta-nixpkgs,
+    agents,
+  } @ inputs:
     flake-utils.lib.eachDefaultSystem (system: let
       pkgs = nixpkgs.legacyPackages.${system};
       pythonPackages = pkgs.python311Packages;
@@ -74,6 +82,12 @@
           license = pkgs.lib.licenses.mit;
         };
       };
+
+      m3taLib = m3ta-nixpkgs.lib.x86_64-linux;
+      rules = m3taLib.opencode-rules.mkOpencodeRules {
+        inherit agents;
+        languages = ["python"];
+      };
     in {
       packages.default = zugferd-service;
       packages.zugferd-service = zugferd-service;
@@ -96,6 +110,11 @@
             ]))
           pkgs.python311Packages.pip
         ];
+
+        inherit (rules) instructions;
+        shellHook = ''
+          ${rules.shellHook}
+        '';
       };
     });
 }