diff --git a/.claude/settings.json b/.claude/settings.json
deleted file mode 100644
index cd5372a..0000000
--- a/.claude/settings.json
+++ /dev/null
@@ -1,19 +0,0 @@
-{
-  "attribution": {
-    "commit": "",
-    "pr": ""
-  },
-  "hooks": {
-    "PostToolUse": [
-      {
-        "matcher": "Write|Edit",
-        "hooks": [
-          {
-            "type": "command",
-            "command": "jq -r '.tool_response.filePath // .tool_input.file_path' | { read -r f; case \"$f\" in *.rb) bin/stree write \"$f\" ;; esac; } 2>/dev/null || true"
-          }
-        ]
-      }
-    ]
-  }
-}
diff --git a/.envrc b/.envrc
deleted file mode 100644
index b50a72f..0000000
--- a/.envrc
+++ /dev/null
@@ -1 +0,0 @@
-export MUTANT_SINCE=HEAD
diff --git a/.githooks/pre-commit b/.githooks/pre-commit
deleted file mode 100755
index 3a43294..0000000
--- a/.githooks/pre-commit
+++ /dev/null
@@ -1,17 +0,0 @@
-#!/usr/bin/env bash
-set -euo pipefail
-
-stash_ref=""
-cleanup() {
-  if [ -n "$stash_ref" ]; then
-    git stash pop --quiet "$stash_ref" || true
-  fi
-}
-trap cleanup EXIT
-
-if ! git diff --quiet || [ -n "$(git ls-files --others --exclude-standard)" ]; then
-  git stash push --keep-index --include-untracked --quiet --message "pre-commit: $(date +%s)"
-  stash_ref="stash@{0}"
-fi
-
-bin/rake
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index ae00924..711e2f3 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -22,10 +22,22 @@ jobs:
         with:
           persist-credentials: false
           fetch-depth: 0
-      - name: Set up Ruby
-        uses: ruby/setup-ruby@v1
+      - name: Install Nix
+        uses: cachix/install-nix-action@v31
         with:
-          ruby-version: '4.0.2'
-          bundler-cache: true
+          extra_nix_config: |
+            accept-flake-config = true
+      - name: Set up cachix
+        uses: cachix/cachix-action@v16
+        with:
+          name: devenv
+      - name: Install devenv
+        run: nix profile install nixpkgs#devenv
+      - name: Cache gems
+        uses: actions/cache@v4
+        with:
+          path: .devenv/state/.bundle
+          key: ${{ runner.os }}-gems-${{ hashFiles('Gemfile.lock') }}
+          restore-keys: ${{ runner.os }}-gems-
       - name: Run the default task
-        run: bin/rake
+        run: devenv shell -- bin/rake
diff --git a/.gitignore b/.gitignore
index eeca105..ca4d092 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,12 @@
+/.claude/settings.json
+/.mcp.json
 /.bundle/
 /.mutant/
 /pkg/
 /tmp/
 /test/pg_regress/results/
+.devenv*
+devenv.local.nix
+devenv.local.yaml
+.pre-commit-config.yaml
+/.githooks/
diff --git a/Gemfile.lock b/Gemfile.lock
index 9c1ddd0..abbd85f 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -313,7 +313,6 @@ CHECKSUMS
   benchmark (0.5.0) sha256=465df122341aedcb81a2a24b4d3bd19b6c67c1530713fd533f3ff034e419236c
   bigdecimal (4.1.2) sha256=53d217666027eab4280346fba98e7d5b66baaae1b9c3c1c0ffe89d48188a3fbd
   builder (3.3.0) sha256=497918d2f9dca528fdca4b88d84e4ef4387256d984b8154e9d5d3fe5a9c8835f
-  bundler (4.0.11) sha256=5bcec0fb78302e48d02ee46f10ee6e6942be647ba5b44a6d1ddfda9a240ce785
   concurrent-ruby (1.3.6) sha256=6b56837e1e7e5292f9864f34b69c5a2cbc75c0cf5338f1ce9903d10fa762d5ab
   connection_pool (3.0.2) sha256=33fff5ba71a12d2aa26cb72b1db8bba2a1a01823559fb01d29eb74c286e62e0a
   crass (1.0.6) sha256=dc516022a56e7b3b156099abc81b6d2b08ea1ed12676ac7a5657617f012bd45d
@@ -396,4 +395,4 @@ CHECKSUMS
   zeitwerk (2.8.2) sha256=7212a61311083c604184b1ea2574b9aa05cd14f855a0841c06985cabe9181d12
 
 BUNDLED WITH
-  4.0.11
+   2.7.2
diff --git a/devenv.lock b/devenv.lock
new file mode 100644
index 0000000..867955b
--- /dev/null
+++ b/devenv.lock
@@ -0,0 +1,197 @@
+{
+  "nodes": {
+    "devenv": {
+      "locked": {
+        "dir": "src/modules",
+        "lastModified": 1782231411,
+        "narHash": "sha256-W/Yhek5L3nc0gaGgMHPrzO6DbLGq7Yb9DKw/kvLwij0=",
+        "owner": "cachix",
+        "repo": "devenv",
+        "rev": "a4fd3348220d96f7602385adff0ace482e720586",
+        "type": "github"
+      },
+      "original": {
+        "dir": "src/modules",
+        "owner": "cachix",
+        "repo": "devenv",
+        "type": "github"
+      }
+    },
+    "flake-compat": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1767039857,
+        "narHash": "sha256-vNpUSpF5Nuw8xvDLj2KCwwksIbjua2LZCqhV1LNRDns=",
+        "owner": "NixOS",
+        "repo": "flake-compat",
+        "rev": "5edf11c44bc78a0d334f6334cdaf7d60d732daab",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "repo": "flake-compat",
+        "type": "github"
+      }
+    },
+    "flake-compat_2": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1767039857,
+        "narHash": "sha256-vNpUSpF5Nuw8xvDLj2KCwwksIbjua2LZCqhV1LNRDns=",
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "rev": "5edf11c44bc78a0d334f6334cdaf7d60d732daab",
+        "type": "github"
+      },
+      "original": {
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "type": "github"
+      }
+    },
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1731533236,
+        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "git-hooks": {
+      "inputs": {
+        "flake-compat": "flake-compat",
+        "gitignore": "gitignore",
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1781733627,
+        "narHash": "sha256-U3yTuGBnmXvXoQI3qkpfEDsn9RovQPAjN7ndRco+3u0=",
+        "owner": "cachix",
+        "repo": "git-hooks.nix",
+        "rev": "3bbec39bc90eadfa031e6f3b77272f3f60803e39",
+        "type": "github"
+      },
+      "original": {
+        "owner": "cachix",
+        "repo": "git-hooks.nix",
+        "type": "github"
+      }
+    },
+    "gitignore": {
+      "inputs": {
+        "nixpkgs": [
+          "git-hooks",
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1709087332,
+        "narHash": "sha256-HG2cCnktfHsKV0s4XW83gU3F57gaTljL9KNSuG6bnQs=",
+        "owner": "hercules-ci",
+        "repo": "gitignore.nix",
+        "rev": "637db329424fd7e46cf4185293b9cc8c88c95394",
+        "type": "github"
+      },
+      "original": {
+        "owner": "hercules-ci",
+        "repo": "gitignore.nix",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "inputs": {
+        "nixpkgs-src": "nixpkgs-src"
+      },
+      "locked": {
+        "lastModified": 1782132010,
+        "narHash": "sha256-ZnAVHdVrotp80iIMm5CSR1fdxPlw7Uwmwxb+O/wsgZ8=",
+        "owner": "cachix",
+        "repo": "devenv-nixpkgs",
+        "rev": "12866ae2dddbc0ab8b329915f8072bb9c75bde89",
+        "type": "github"
+      },
+      "original": {
+        "owner": "cachix",
+        "ref": "rolling",
+        "repo": "devenv-nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-ruby": {
+      "inputs": {
+        "flake-compat": "flake-compat_2",
+        "flake-utils": "flake-utils",
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1782291298,
+        "narHash": "sha256-s5qd1ZWKoc8m6dnTvcHTMWerE8xXOSG82Vgp7eIPesk=",
+        "owner": "bobvanderlinden",
+        "repo": "nixpkgs-ruby",
+        "rev": "5a59e45e96465645c00422fedf5e62e337f6cfea",
+        "type": "github"
+      },
+      "original": {
+        "owner": "bobvanderlinden",
+        "repo": "nixpkgs-ruby",
+        "type": "github"
+      }
+    },
+    "nixpkgs-src": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1781607440,
+        "narHash": "sha256-rxO+uc/KFbSJp+pgyXRuAX6QlG9hJdnt0BXpEQRXY+U=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "3e41b24abd260e8f71dbe2f5737d24122f972158",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "devenv": "devenv",
+        "git-hooks": "git-hooks",
+        "nixpkgs": "nixpkgs",
+        "nixpkgs-ruby": "nixpkgs-ruby"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
\ No newline at end of file
diff --git a/devenv.nix b/devenv.nix
new file mode 100644
index 0000000..50f0c47
--- /dev/null
+++ b/devenv.nix
@@ -0,0 +1,54 @@
+{ pkgs, lib, ... }:
+
+{
+  languages.ruby.enable = true;
+  languages.ruby.version = "4.0.5";
+
+  packages = [
+    pkgs.postgresql_18
+    pkgs.postgresql_18.pg_config
+    pkgs.pgformatter
+    pkgs.jq
+    pkgs.libyaml
+  ];
+
+  env.PG_REGRESS = "${pkgs.postgresql_18.dev}/lib/pgxs/src/test/regress/pg_regress";
+
+  enterShell = ''
+    export MUTANT_SINCE="''${MUTANT_SINCE:-HEAD}"
+    bundle install --quiet
+  '';
+
+  enterTest = "bin/rake";
+
+  tasks = {
+    "app:format".exec = "bin/rake format";
+    "app:test".exec = "bin/rake test";
+    "app:mutate".exec = "bin/mutant run";
+    "app:pg-regress".exec = "bin/rake pg_regress";
+    "app:check".exec = "bin/rake"; # default: test + mutate_since
+  };
+
+  git-hooks.hooks.rake = {
+    enable = true;
+    name = "rake (test + mutate_since)";
+    entry = "${pkgs.writeShellScript "rake-precommit" ''
+      export MUTANT_SINCE="''${MUTANT_SINCE:-HEAD}"
+      exec bin/rake
+    ''}";
+    pass_filenames = false;
+    language = "system";
+    stages = [ "pre-commit" ];
+  };
+
+  claude.code.enable = true;
+  claude.code.hooks.git-hooks-run.enable = false;
+  claude.code.hooks.format-ruby = {
+    name = "Format Ruby with syntax_tree";
+    hookType = "PostToolUse";
+    matcher = "Write|Edit";
+    command = ''
+      jq -r '.tool_response.filePath // .tool_input.file_path' | { read -r f; case "$f" in *.rb) bin/stree write "$f" ;; esac; } 2>/dev/null || true
+    '';
+  };
+}
diff --git a/devenv.yaml b/devenv.yaml
new file mode 100644
index 0000000..5a3d24b
--- /dev/null
+++ b/devenv.yaml
@@ -0,0 +1,13 @@
+inputs:
+  nixpkgs:
+    url: github:cachix/devenv-nixpkgs/rolling
+  git-hooks:
+    url: github:cachix/git-hooks.nix
+    inputs:
+      nixpkgs:
+        follows: nixpkgs
+  nixpkgs-ruby:
+    url: github:bobvanderlinden/nixpkgs-ruby
+    inputs:
+      nixpkgs:
+        follows: nixpkgs