fix: make pytest_typeguard a no-op on Python 3.14

typeguard 2.13.3 uses ast.Str at import time, which was removed in
Python 3.14. The pytest_typeguard plugin imported it eagerly at module
load, crashing pytest session start on 3.14 and taking down test
collection for the entire suite.

This is a surgical fix: defer the typeguard import inside
pytest_sessionstart and skip the install_import_hook call on Python
3.14+. Behavior on Python 3.13 and below is unchanged.

Proper fix (typeguard 4.x migration) remains tracked by the existing
TODO comment on the typeguard pin in pyproject.toml.

Author: jstvz

cumulusci/tests/pytest_plugins/pytest_typeguard.py

@@ -1,5 +1,16 @@
-from typeguard.importhook import install_import_hook
+import sys
+import warnings
 
 
 def pytest_sessionstart(session):
+    if sys.version_info >= (3, 14):
+        warnings.warn(
+            "pytest_typeguard plugin is disabled on Python 3.14+ until typeguard "
+            "is upgraded to 4.x (typeguard 2.13.3 uses removed ast.Str). "
+            "See pyproject.toml TODO.",
+            stacklevel=2,
+        )
+        return
+    from typeguard.importhook import install_import_hook
+
     install_import_hook(packages=["cumulusci"])

cumulusci/tests/pytest_plugins/test_pytest_typeguard.py

@@ -0,0 +1,67 @@
+"""Pin tests for the pytest_typeguard plugin's Python 3.14 compatibility shim.
+
+typeguard 2.13.3 is pinned in pyproject.toml (TODO: upgrade to v4) and its
+import hook references ast.Str, which was removed in Python 3.14. The plugin
+must skip installing the hook on Python 3.14+ so pytest's session start does
+not crash and take the entire suite down.
+
+These tests use mocks to simulate both Python version regimes so they pass
+under any interpreter that has a typeguard package available.
+"""
+
+import importlib
+import sys
+import types
+from unittest import mock
+
+
+def _make_fake_typeguard():
+    """Build a fake `typeguard.importhook` module exposing a Mock install_import_hook."""
+    fake_install_import_hook = mock.Mock()
+    fake_typeguard = types.ModuleType("typeguard")
+    fake_importhook = types.ModuleType("typeguard.importhook")
+    fake_importhook.install_import_hook = fake_install_import_hook
+    fake_typeguard.importhook = fake_importhook
+    return fake_typeguard, fake_importhook, fake_install_import_hook
+
+
+def _reload_plugin():
+    from cumulusci.tests.pytest_plugins import pytest_typeguard
+
+    importlib.reload(pytest_typeguard)
+    return pytest_typeguard
+
+
+def test_pytest_sessionstart_is_noop_on_py314():
+    """On Python 3.14+, pytest_sessionstart must not call install_import_hook."""
+    fake_typeguard, fake_importhook, fake_install_import_hook = _make_fake_typeguard()
+
+    with (
+        mock.patch.dict(
+            sys.modules,
+            {"typeguard": fake_typeguard, "typeguard.importhook": fake_importhook},
+        ),
+        mock.patch.object(sys, "version_info", (3, 14, 0, "final", 0)),
+    ):
+        plugin = _reload_plugin()
+        result = plugin.pytest_sessionstart(None)
+
+    assert result is None
+    fake_install_import_hook.assert_not_called()
+
+
+def test_pytest_sessionstart_installs_hook_on_py313():
+    """On Python <= 3.13, pytest_sessionstart must install the typeguard import hook."""
+    fake_typeguard, fake_importhook, fake_install_import_hook = _make_fake_typeguard()
+
+    with (
+        mock.patch.dict(
+            sys.modules,
+            {"typeguard": fake_typeguard, "typeguard.importhook": fake_importhook},
+        ),
+        mock.patch.object(sys, "version_info", (3, 13, 0, "final", 0)),
+    ):
+        plugin = _reload_plugin()
+        plugin.pytest_sessionstart(None)
+
+    fake_install_import_hook.assert_called_once_with(packages=["cumulusci"])