test: switch zero-dep install test to uv venv

tests/test_zero_dep_install.py

@@ -9,42 +9,60 @@
 
 This guards the architectural contract documented in ``tech.md``
 ADR-002. Marked ``slow`` because it creates a real venv.
+
+Uses ``uv venv`` + ``uv pip`` rather than stdlib ``venv``/``pip`` because
+``ensurepip`` aborts on some Python builds (observed on cpython 3.11.14
+macOS-aarch64).
 """
 
 from __future__ import annotations
 
+import shutil
 import subprocess
 import sys
-import venv
 from pathlib import Path
 
 import pytest
 
 REPO_ROOT = Path(__file__).resolve().parent.parent
 
+_UV = shutil.which("uv")
 
-@pytest.mark.slow
-@pytest.mark.skipif(
-    sys.platform.startswith("win"),
-    reason="venv layout differs on Windows; covered on Linux/macOS",
+_requires_uv = pytest.mark.skipif(
+    _UV is None,
+    reason="uv is required to build the isolated test venv (stdlib ensurepip is unreliable)",
 )
-def test_attune_help_imports_without_authoring_extra(tmp_path: Path) -> None:
-    venv_dir = tmp_path / "venv"
-    venv.create(venv_dir, with_pip=True)
-    py = venv_dir / "bin" / "python"
-    pip = venv_dir / "bin" / "pip"
 
+
+def _make_venv(venv_dir: Path) -> Path:
+    """Create a venv at ``venv_dir`` via ``uv venv`` and return its python."""
     subprocess.run(
-        [str(pip), "install", "--quiet", "python-frontmatter"],
+        [_UV, "venv", "--quiet", str(venv_dir)],
         check=True,
         capture_output=True,
     )
+    return venv_dir / "bin" / "python"
+
+
+def _install(py: Path, *args: str) -> None:
     subprocess.run(
-        [str(pip), "install", "--quiet", "--no-deps", "-e", str(REPO_ROOT)],
+        [_UV, "pip", "install", "--quiet", "--python", str(py), *args],
         check=True,
         capture_output=True,
     )
 
+
+@pytest.mark.slow
+@_requires_uv
+@pytest.mark.skipif(
+    sys.platform.startswith("win"),
+    reason="venv layout differs on Windows; covered on Linux/macOS",
+)
+def test_attune_help_imports_without_authoring_extra(tmp_path: Path) -> None:
+    py = _make_venv(tmp_path / "venv")
+    _install(py, "python-frontmatter")
+    _install(py, "--no-deps", "-e", str(REPO_ROOT))
+
     base = subprocess.run(
         [str(py), "-c", "import attune_help; print('ok')"],
         capture_output=True,
@@ -55,6 +73,7 @@ def test_attune_help_imports_without_authoring_extra(tmp_path: Path) -> None:
 
 
 @pytest.mark.slow
+@_requires_uv
 @pytest.mark.skipif(
     sys.platform.startswith("win"),
     reason="venv layout differs on Windows; covered on Linux/macOS",
@@ -69,21 +88,9 @@ def test_attune_help_imports_without_authoring_extra(tmp_path: Path) -> None:
     ],
 )
 def test_shim_imports_fail_helpfully_without_authoring(tmp_path: Path, shim_module: str) -> None:
-    venv_dir = tmp_path / "venv"
-    venv.create(venv_dir, with_pip=True)
-    py = venv_dir / "bin" / "python"
-    pip = venv_dir / "bin" / "pip"
-
-    subprocess.run(
-        [str(pip), "install", "--quiet", "python-frontmatter"],
-        check=True,
-        capture_output=True,
-    )
-    subprocess.run(
-        [str(pip), "install", "--quiet", "--no-deps", "-e", str(REPO_ROOT)],
-        check=True,
-        capture_output=True,
-    )
+    py = _make_venv(tmp_path / "venv")
+    _install(py, "python-frontmatter")
+    _install(py, "--no-deps", "-e", str(REPO_ROOT))
 
     result = subprocess.run(
         [str(py), "-c", f"import {shim_module}"],