diff --git a/.github/workflows/quality-gate.yml b/.github/workflows/quality-gate.yml
index 3dcea84..14dfab7 100644
--- a/.github/workflows/quality-gate.yml
+++ b/.github/workflows/quality-gate.yml
@@ -56,8 +56,13 @@ jobs:
         run: uv run mypy src/nasde_toolkit/
 
   test:
-    name: Unit tests (pytest)
-    runs-on: ubuntu-latest
+    name: Unit tests (pytest) — ${{ matrix.os }} / py${{ matrix.python }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest]
+        python: ["3.12", "3.13"]
     steps:
       - uses: actions/checkout@v4
 
@@ -67,7 +72,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v5
         with:
-          python-version: "3.12"
+          python-version: ${{ matrix.python }}
 
       - name: Install dependencies
         run: uv sync --extra dev
diff --git a/tests/test_evaluator_backends.py b/tests/test_evaluator_backends.py
index efe865e..1d4150e 100644
--- a/tests/test_evaluator_backends.py
+++ b/tests/test_evaluator_backends.py
@@ -223,7 +223,7 @@ def test_codex_backend_validate_auth_succeeds_with_chatgpt_oauth(
     codex_home.mkdir()
     auth_file = codex_home / "auth.json"
     auth_file.write_text('{"auth_mode": "chatgpt", "tokens": {"access_token": "tok"}}')
-    monkeypatch.setenv("HOME", str(tmp_path))
+    monkeypatch.setattr("pathlib.Path.home", lambda: tmp_path)
     backend = CodexSubprocessBackend()
     backend.validate_auth()
 
@@ -231,7 +231,7 @@ def test_codex_backend_validate_auth_succeeds_with_chatgpt_oauth(
 def test_codex_backend_validate_auth_fails_without_credentials(monkeypatch: pytest.MonkeyPatch, tmp_path: Path) -> None:
     monkeypatch.delenv("OPENAI_API_KEY", raising=False)
     monkeypatch.delenv("CODEX_API_KEY", raising=False)
-    monkeypatch.setenv("HOME", str(tmp_path))
+    monkeypatch.setattr("pathlib.Path.home", lambda: tmp_path)
     backend = CodexSubprocessBackend()
     with pytest.raises(SystemExit):
         backend.validate_auth()
@@ -263,7 +263,7 @@ def test_codex_backend_env_strips_api_keys_when_oauth_present(
     codex_home = tmp_path / ".codex"
     codex_home.mkdir()
     (codex_home / "auth.json").write_text('{"auth_mode": "chatgpt", "tokens": {"access_token": "tok"}}')
-    monkeypatch.setenv("HOME", str(tmp_path))
+    monkeypatch.setattr("pathlib.Path.home", lambda: tmp_path)
     monkeypatch.setenv("CODEX_API_KEY", "sk-stale-key-from-dotenv")
     monkeypatch.delenv("OPENAI_API_KEY", raising=False)
 
@@ -278,7 +278,7 @@ def test_codex_backend_env_promotes_codex_key_to_openai_key(
     monkeypatch: pytest.MonkeyPatch,
     tmp_path: Path,
 ) -> None:
-    monkeypatch.setenv("HOME", str(tmp_path))
+    monkeypatch.setattr("pathlib.Path.home", lambda: tmp_path)
     monkeypatch.setenv("CODEX_API_KEY", "sk-codex-key")
     monkeypatch.delenv("OPENAI_API_KEY", raising=False)
 
@@ -296,7 +296,7 @@ def test_codex_backend_env_preserves_openai_key_priority(
     codex_home = tmp_path / ".codex"
     codex_home.mkdir()
     (codex_home / "auth.json").write_text('{"auth_mode": "chatgpt", "tokens": {"access_token": "tok"}}')
-    monkeypatch.setenv("HOME", str(tmp_path))
+    monkeypatch.setattr("pathlib.Path.home", lambda: tmp_path)
     monkeypatch.setenv("OPENAI_API_KEY", "sk-explicit-openai-key")
     monkeypatch.setenv("CODEX_API_KEY", "sk-stale-codex-key")