diff --git a/.gitignore b/.gitignore
index e1559e2..7075402 100644
--- a/.gitignore
+++ b/.gitignore
@@ -24,6 +24,7 @@ wheels/
 venv/
 ENV/
 env/
+.direnv/
 
 # IDE
 .vscode/
@@ -40,3 +41,17 @@ htmlcov/
 .sisyphus/boulder.json
 .sisyphus/notepads/*/issues.md
 .sisyphus/notepads/*/problems.md
+
+# Opencode rules
+.opencode-rules/
+opencode.json
+.todos/
+
+# Sidecar worktree state files
+.sidecar/
+.sidecar-agent
+.sidecar-task
+.sidecar-pr
+.sidecar-start.sh
+.sidecar-base
+.td-root
diff --git a/AGENTS.md b/AGENTS.md
index 07746af..1976565 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -1,5 +1,10 @@
 # AGENTS.md - Agent Development Guide
 
+## MANDATORY: Use td for Task Management
+
+You must run td usage --new-session at conversation start (or after /clear) to see current work.
+Use td usage -q for subsequent reads.
+
 This document provides context and guidelines for agentic coding agents working on the zugferd-service repository.
 
 ## Project Overview
diff --git a/flake.lock b/flake.lock
index 668ac53..704b309 100644
--- a/flake.lock
+++ b/flake.lock
@@ -1,5 +1,21 @@
 {
   "nodes": {
+    "agents": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1771353084,
+        "narHash": "sha256-QsrA7+md+bw1ACQeuvDn2mE5X11gM0hqVGse58spedA=",
+        "ref": "refs/heads/master",
+        "rev": "5b204c95e419eb75b04c5f85e1bd56ed56a5abe4",
+        "revCount": 60,
+        "type": "git",
+        "url": "https://code.m3ta.dev/m3tam3re/AGENTS"
+      },
+      "original": {
+        "type": "git",
+        "url": "https://code.m3ta.dev/m3tam3re/AGENTS"
+      }
+    },
     "flake-utils": {
       "inputs": {
         "systems": "systems"
@@ -18,7 +34,59 @@
         "type": "github"
       }
     },
+    "m3ta-nixpkgs": {
+      "inputs": {
+        "nixpkgs": "nixpkgs",
+        "nixpkgs-master": "nixpkgs-master",
+        "opencode": "opencode"
+      },
+      "locked": {
+        "lastModified": 1771355771,
+        "narHash": "sha256-Uhq6aMCuzKqC2UIAbEkx+LQS77MGEVDEL7zpfoW6VB8=",
+        "ref": "refs/heads/master",
+        "rev": "dc206b13e256941298868d559fff9be31d7e0e34",
+        "revCount": 119,
+        "type": "git",
+        "url": "https://code.m3ta.dev/m3tam3re/nixpkgs"
+      },
+      "original": {
+        "type": "git",
+        "url": "https://code.m3ta.dev/m3tam3re/nixpkgs"
+      }
+    },
     "nixpkgs": {
+      "locked": {
+        "lastModified": 1770562336,
+        "narHash": "sha256-ub1gpAONMFsT/GU2hV6ZWJjur8rJ6kKxdm9IlCT0j84=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "d6c71932130818840fc8fe9509cf50be8c64634f",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-master": {
+      "locked": {
+        "lastModified": 1770917518,
+        "narHash": "sha256-XSwv/tVrNo/L8SPH8Lx9xZH1PrZd/3Z3J/0SH7Xertg=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "3f4a3c08f2f318ee29fc8a2689f390071a94aaf0",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "master",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs_2": {
       "locked": {
         "lastModified": 1770115704,
         "narHash": "sha256-KHFT9UWOF2yRPlAnSXQJh6uVcgNcWlFqqiAZ7OVlHNc=",
@@ -34,10 +102,34 @@
         "type": "github"
       }
     },
+    "opencode": {
+      "inputs": {
+        "nixpkgs": [
+          "m3ta-nixpkgs",
+          "nixpkgs-master"
+        ]
+      },
+      "locked": {
+        "lastModified": 1771271829,
+        "narHash": "sha256-43vPMyO7DsAgKrh0Wmt7jLDYCWUsaj30nBITreyYgX8=",
+        "owner": "anomalyco",
+        "repo": "opencode",
+        "rev": "d8c25bfeb44771cc3a3ba17bf8de6ad2add9de2c",
+        "type": "github"
+      },
+      "original": {
+        "owner": "anomalyco",
+        "ref": "v1.2.6",
+        "repo": "opencode",
+        "type": "github"
+      }
+    },
     "root": {
       "inputs": {
+        "agents": "agents",
         "flake-utils": "flake-utils",
-        "nixpkgs": "nixpkgs"
+        "m3ta-nixpkgs": "m3ta-nixpkgs",
+        "nixpkgs": "nixpkgs_2"
       }
     },
     "systems": {
diff --git a/flake.nix b/flake.nix
index e9ca2b0..9fc1b00 100644
--- a/flake.nix
+++ b/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}
+        '';
       };
     });
 }