chore(dev): add nix-unit

dev/flake-module.nix

@@ -4,6 +4,7 @@
   imports = [
     inputs.pre-commit-hooks-nix.flakeModule
     inputs.hercules-ci-effects.flakeModule # herculesCI attr
+    inputs.nix-unit.modules.flake.default
   ];
   systems = [ "x86_64-linux" "aarch64-darwin" ];
 
@@ -21,6 +22,7 @@
 
     devShells.default = pkgs.mkShell {
       nativeBuildInputs = [
+        config.nix-unit.package
         pkgs.nixpkgs-fmt
         pkgs.hci
       ];
@@ -40,6 +42,10 @@
       let tests = import ./tests/eval-tests.nix { flake-parts = self; };
       in tests.runTests pkgs.emptyFile // { internals = tests; };
 
+    # nix-unit evaluates the flake, which triggers the dev partition via
+    # flake-compat, requiring network to fetch dev inputs.
+    nix-unit.allowNetwork = true;
+
   };
   flake = {
     # for repl exploration / debug

dev/flake.lock

@@ -76,6 +76,49 @@
         "type": "github"
       }
     },
+    "nix-github-actions": {
+      "inputs": {
+        "nixpkgs": [
+          "nix-unit",
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1737420293,
+        "narHash": "sha256-F1G5ifvqTpJq7fdkT34e/Jy9VCyzd5XfJ9TO8fHhJWE=",
+        "owner": "nix-community",
+        "repo": "nix-github-actions",
+        "rev": "f4158fa080ef4503c8f4c820967d946c2af31ec9",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "nix-github-actions",
+        "type": "github"
+      }
+    },
+    "nix-unit": {
+      "inputs": {
+        "nix-github-actions": "nix-github-actions",
+        "nixpkgs": [
+          "nixpkgs"
+        ],
+        "treefmt-nix": "treefmt-nix"
+      },
+      "locked": {
+        "lastModified": 1777114263,
+        "narHash": "sha256-vZfRXBDC9FTO2Vpz8TroVMqOYqp+hcVk6Nwx6+kRN1Q=",
+        "owner": "nix-community",
+        "repo": "nix-unit",
+        "rev": "02e6597889281382303cbb7973748f04f2940e1a",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "nix-unit",
+        "type": "github"
+      }
+    },
     "nixpkgs": {
       "locked": {
         "lastModified": 1775710090,
@@ -132,9 +175,31 @@
     "root": {
       "inputs": {
         "hercules-ci-effects": "hercules-ci-effects",
+        "nix-unit": "nix-unit",
         "nixpkgs": "nixpkgs_2",
         "pre-commit-hooks-nix": "pre-commit-hooks-nix"
       }
+    },
+    "treefmt-nix": {
+      "inputs": {
+        "nixpkgs": [
+          "nix-unit",
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1775636079,
+        "narHash": "sha256-pc20NRoMdiar8oPQceQT47UUZMBTiMdUuWrYu2obUP0=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "790751ff7fd3801feeaf96d7dc416a8d581265ba",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "type": "github"
+      }
     }
   },
   "root": "root",

dev/flake.nix

@@ -10,6 +10,8 @@
     pre-commit-hooks-nix.url = "github:cachix/pre-commit-hooks.nix";
     pre-commit-hooks-nix.inputs.nixpkgs.follows = "nixpkgs";
     hercules-ci-effects.url = "github:hercules-ci/hercules-ci-effects";
+    nix-unit.url = "github:nix-community/nix-unit";
+    nix-unit.inputs.nixpkgs.follows = "nixpkgs";
   };
 
   outputs = { ... }: