test(cron): two invariants plus the Windows lane marker (#122183)

platforms("windows") instead of a bare skipif: list_os_marked_tests.py
gates the Windows lane on that marker, so the skipif version ran on no
CI lane at all -- the antipattern root AGENTS.md calls out.

Four tests collapse to the two invariants that actually matter: the
committed generation wins, and no-generation/unreadable-record both
fall through to the handed venv. The legacy non-managed test is gone --
it passes on main by design, and the fall-through test's positive
control now covers that path inside the managed arm.

(cherry picked from commit 30c649f16bce08eeaabd5a407ae0429cf422556a)

tests/cron/test_cron_windows_venv_abi.py

@@ -0,0 +1,124 @@
+"""Windows cron scripts resolve their dependency tree, and fall through when there is none.
+
+``cron/scheduler_script.py::_windows_cron_python_invocation`` answers "which interpreter and
+which site-packages?" for a cron script child. On a PM-managed install it read the dependency
+tree through ``pm.environments.selected_venv``, which falls back to ``base_venv`` and answers
+the leftover pre-PM ``<root>/venv`` when no generation is recorded. That tree is built for
+whichever interpreter created it, so overlaying it on the managed store Python loads a cp311
+``pydantic_core`` on 3.14 and every script dies with
+``ModuleNotFoundError: No module named 'pydantic_core._pydantic_core'`` — the cron sibling of
+the gateway crash in #122183/#123650, which no PR covered.
+
+Two invariants:
+
+1. With a generation committed, that generation is the tree the child gets — never the in-tree
+   venv.
+2. With NO generation, or a record too corrupt to read, the managed branch falls through to the
+   uv overlay: the handed venv keeps its own interpreter and its own site-packages. Handing back
+   the bare store Python instead would be worse than main (``_require_own_dependencies`` refuses
+   it with "hermes pm repair" and a cron script has no bootstrap to refuse cleanly), and it
+   strips the overlay's site-packages entry, warning on every spawn.
+"""
+
+import os
+import sys
+from pathlib import Path
+
+import pytest
+
+pytestmark = pytest.mark.platforms("windows")
+
+
+def _write_venv(venv: Path, base: Path, *, version: str | None = None) -> Path:
+    """A fake Windows venv with the ``Scripts/python.exe`` shim a cron child is handed."""
+    (venv / "Lib" / "site-packages").mkdir(parents=True, exist_ok=True)
+    (venv / "Scripts").mkdir(parents=True, exist_ok=True)
+    base.mkdir(parents=True, exist_ok=True)
+    (venv / "Scripts" / "python.exe").write_text("", encoding="utf-8")
+    (base / "python.exe").write_text("", encoding="utf-8")
+    lines = [f"home = {base}", "uv = 0.11.14"]
+    if version:
+        lines.append(f"version_info = {version}")
+    (venv / "pyvenv.cfg").write_text("\n".join(lines) + "\n", encoding="utf-8")
+    return venv
+
+
+def _site_packages_in(env_overlay: dict) -> Path | None:
+    for entry in env_overlay.get("PYTHONPATH", "").split(os.pathsep):
+        if Path(entry).name == "site-packages":
+            return Path(entry)
+    return None
+
+
+def _raise_runtime_error(_root):
+    raise RuntimeError("cannot read dependency environment: facts.json")
+
+
+def test_managed_install_uses_the_committed_generation_not_the_in_tree_venv(
+    tmp_path, monkeypatch,
+):
+    """The committed generation wins; the leftover pre-PM venv never reaches the child."""
+    from cron import scheduler_script as sched_script
+
+    stale = _write_venv(tmp_path / "repo" / "venv", tmp_path / "base")
+    committed = _write_venv(
+        tmp_path / "installs" / "gen" / "venv", tmp_path / "genbase",
+        version=f"{sys.version_info[0]}.{sys.version_info[1]}.7",
+    )
+    store = tmp_path / "store" / "python.exe"
+    store.parent.mkdir(parents=True)
+    store.write_text("", encoding="utf-8")
+    child = _write_venv(tmp_path / "child", tmp_path / "childbase")
+
+    monkeypatch.setattr("hermes_cli._launchers.resolve_store_python", lambda _root: store)
+    monkeypatch.setattr("pm.environments.committed_venv", lambda _root: committed)
+    monkeypatch.setattr("pm.environments.selected_venv", lambda _root: stale)
+
+    interpreter, env_overlay = sched_script._windows_cron_python_invocation(
+        str(child / "Scripts" / "python.exe")
+    )
+
+    assert interpreter == str(store)
+    overlay = _site_packages_in(env_overlay)
+    assert overlay is not None, "the committed generation must supply a site-packages entry"
+    assert overlay == committed / "Lib" / "site-packages"
+    assert not overlay.is_relative_to(stale)
+
+
+def test_managed_install_without_a_generation_falls_through_to_the_handed_venv(
+    tmp_path, monkeypatch,
+):
+    """No generation, or an unreadable record: the handed venv keeps its own packages.
+
+    Both arms must land identically — the child gets its own base interpreter and its own
+    site-packages, not the bare store Python, which cannot serve a script with nothing
+    committed. Positive control for the fall-through: the handed venv here IS a uv venv
+    carrying its own site-packages, exactly the case that worked on main.
+    """
+    from cron import scheduler_script as sched_script
+
+    stale = _write_venv(tmp_path / "repo" / "venv", tmp_path / "base")
+    store = tmp_path / "store" / "python.exe"
+    store.parent.mkdir(parents=True)
+    store.write_text("", encoding="utf-8")
+
+    for label, committed in (("none", lambda _root: None),
+                             ("unreadable", _raise_runtime_error)):
+        case = tmp_path / label
+        child = _write_venv(case / "child", case / "childbase")
+        monkeypatch.setattr("hermes_cli._launchers.resolve_store_python",
+                            lambda _root, s=store: s)
+        monkeypatch.setattr("pm.environments.committed_venv", committed)
+        monkeypatch.setattr("pm.environments.selected_venv", lambda _root, t=stale: t)
+
+        interpreter, env_overlay = sched_script._windows_cron_python_invocation(
+            str(child / "Scripts" / "python.exe")
+        )
+
+        assert interpreter == str(case / "childbase" / "python.exe"), label
+        assert env_overlay["VIRTUAL_ENV"] == str(child), label
+        overlay = _site_packages_in(env_overlay)
+        assert overlay is not None, f"{label}: the overlay must carry site-packages"
+        assert overlay == child / "Lib" / "site-packages", label
+        assert not overlay.is_relative_to(stale), label
+        assert interpreter != str(store), label