fix: relax start_new_session assertion for systemd scope path

The windows-compat change-detector checked for the literal string
'start_new_session=True', but the systemd scope isolation path
conditionally uses start_new_session=False (the scope creates its own
session/cgroup). Assert 'start_new_session=' instead — the value may
now be a variable.

tests/tools/test_windows_compat.py

@@ -51,17 +51,23 @@ class TestStartNewSession:
 
     @pytest.mark.parametrize("relpath", GUARDED_FILES)
     def test_uses_start_new_session(self, relpath):
-        """Each guarded file must use start_new_session=True for process isolation."""
+        """Each guarded file must use start_new_session instead of preexec_fn.
+
+        The value may be a variable (e.g. ``popen_start_new_session``) when
+        the spawn conditionally uses ``systemd-run --scope`` which creates its
+        own session/cgroup — in that case ``start_new_session=False`` is
+        correct and a literal ``True`` would mask scope-creation failures.
+        """
         filepath = PROJECT_ROOT / relpath
         if not filepath.exists():
             pytest.skip(f"{relpath} not found")
         source = filepath.read_text(encoding="utf-8")
-        # Files should use start_new_session=True, not preexec_fn
+        # Files should use start_new_session, not preexec_fn
         assert "preexec_fn" not in source, (
             f"{relpath} still uses preexec_fn; use start_new_session=True instead"
         )
-        assert "start_new_session=True" in source, (
-            f"{relpath} missing start_new_session=True in Popen call"
+        assert "start_new_session=" in source, (
+            f"{relpath} missing start_new_session= in Popen call"
         )