test(cli): cover parent-death signal registration and SIGTERM fallback

Unit tests for _enable_parent_death_signal (source-install/no-op gating,
prctl registration, reparenting race, prctl failure) and the early
cleanup-aware SIGTERM fallback handler (cleanup with/without state).

tests/test_parent_death_signal.py

@@ -0,0 +1,115 @@
+"""Tests for the Linux parent-death signal helper in interface/main.py."""
+
+from __future__ import annotations
+
+import os
+import signal
+from unittest import mock
+
+from strix.interface.main import (
+    _enable_parent_death_signal,
+    _install_cleanup_sigterm_handler,
+)
+
+
+def _ctypes_fixture() -> tuple[mock.Mock, mock.Mock, mock._patch]:
+    """Return (ctypes_mock, libc_mock, sysmods_patch) for intercepting ctypes.
+
+    ``_enable_parent_death_signal`` binds ``ctypes`` as a function-local name via
+    ``import ctypes``, so patching the module attribute does not intercept it.
+    Replacing the module in ``sys.modules`` does.
+    """
+
+    ctypes_mock = mock.Mock()
+    libc_mock = ctypes_mock.CDLL.return_value
+    return ctypes_mock, libc_mock, mock.patch.dict("sys.modules", {"ctypes": ctypes_mock})
+
+
+@mock.patch("strix.interface.main.is_binary_install", return_value=False)
+def test_noop_for_source_install(_mock_binary: mock.Mock) -> None:
+    ctypes_mock, _, sysmods = _ctypes_fixture()
+    with mock.patch("strix.interface.main.sys.platform", "linux"), sysmods:
+        _enable_parent_death_signal()
+        ctypes_mock.CDLL.assert_not_called()
+
+
+@mock.patch("strix.interface.main.is_binary_install", return_value=True)
+def test_noop_for_non_linux(_mock_binary: mock.Mock) -> None:
+    ctypes_mock, _, sysmods = _ctypes_fixture()
+    with mock.patch("strix.interface.main.sys.platform", "darwin"), sysmods:
+        _enable_parent_death_signal()
+        ctypes_mock.CDLL.assert_not_called()
+
+
+@mock.patch("strix.interface.main.is_binary_install", return_value=True)
+def test_registers_pdeathsig_when_frozen(_mock_binary: mock.Mock) -> None:
+    _, libc_mock, sysmods = _ctypes_fixture()
+    libc_mock.prctl.return_value = 0
+    with (
+        mock.patch("strix.interface.main.sys.platform", "linux"),
+        mock.patch("strix.interface.main.os.getppid", return_value=1234),
+        mock.patch("strix.interface.main.os.kill") as mock_kill,
+        sysmods,
+    ):
+        _enable_parent_death_signal()
+        libc_mock.prctl.assert_called_once_with(1, signal.SIGTERM)
+        mock_kill.assert_not_called()
+
+
+@mock.patch("strix.interface.main.is_binary_install", return_value=True)
+def test_self_terminates_when_parent_died_before_registration(
+    _mock_binary: mock.Mock,
+) -> None:
+    _, libc_mock, sysmods = _ctypes_fixture()
+    libc_mock.prctl.return_value = 0
+    with (
+        mock.patch("strix.interface.main.sys.platform", "linux"),
+        mock.patch("strix.interface.main.os.getppid", side_effect=[1234, 1]),
+        mock.patch("strix.interface.main.os.kill") as mock_kill,
+        sysmods,
+    ):
+        _enable_parent_death_signal()
+        mock_kill.assert_called_once_with(os.getpid(), signal.SIGTERM)
+
+
+@mock.patch("strix.interface.main.is_binary_install", return_value=True)
+def test_warns_and_returns_when_prctl_fails(_mock_binary: mock.Mock) -> None:
+    _, libc_mock, sysmods = _ctypes_fixture()
+    libc_mock.prctl.return_value = -1
+    with (
+        mock.patch("strix.interface.main.sys.platform", "linux"),
+        mock.patch("strix.interface.main.os.getppid", return_value=1234),
+        mock.patch("strix.interface.main.os.kill") as mock_kill,
+        sysmods,
+    ):
+        _enable_parent_death_signal()
+        libc_mock.prctl.assert_called_once_with(1, signal.SIGTERM)
+        mock_kill.assert_not_called()
+
+
+def test_cleanup_sigterm_handler_cleans_state_and_exits() -> None:
+    with mock.patch("strix.interface.main.signal.signal") as mock_signal:
+        _install_cleanup_sigterm_handler()
+    handler = mock_signal.call_args.args[1]
+
+    state = mock.Mock()
+    with (
+        mock.patch("strix.report.state.get_global_report_state", return_value=state),
+        mock.patch("sys.exit") as mock_exit,
+    ):
+        handler(signal.SIGTERM, None)
+        state.cleanup.assert_called_once_with(status="interrupted")
+        mock_exit.assert_called_once_with(1)
+
+
+def test_cleanup_sigterm_handler_exits_without_state() -> None:
+    with mock.patch("strix.interface.main.signal.signal") as mock_signal:
+        _install_cleanup_sigterm_handler()
+    handler = mock_signal.call_args.args[1]
+
+    with (
+        mock.patch("strix.report.state.get_global_report_state", return_value=None),
+        mock.patch("sys.exit") as mock_exit,
+    ):
+        handler(signal.SIGTERM, None)
+        mock_exit.assert_called_once_with(1)