fix(ci): run GUI test under pyqt5 instead of skipping

.github/workflows/main.yml

@@ -52,6 +52,26 @@ jobs:
           sudo apt install libxkbcommon-x11-0 xvfb libxcb-icccm4 libxcb-image0 libxcb-keysyms1 libxcb-randr0 libxcb-render-util0 libxcb-xinerama0 libxcb-xfixes0 x11-utils
           /sbin/start-stop-daemon --start --quiet --pidfile /tmp/custom_xvfb_99.pid --make-pidfile --background --exec /usr/bin/Xvfb -- :99 -screen 0 1920x1200x24 -ac +extension GLX
       - name: Run the tests
-        # test_HighContentScreeningGui.py: PySide6 QObject double-init bug (separate issue)
+        # SQUID_PYTEST_HARD_EXIT: the suite intermittently segfaults during
+        # interpreter shutdown AFTER all tests pass (Qt destructor order vs
+        # Python GC — the same crash main_hcs.py avoids with os._exit(); seen
+        # on master in 3 of the 15 runs before 2026-07-13). The conftest hook
+        # hard-exits with pytest's real status once the session is complete,
+        # so real test failures still fail the step.
         run: python3 -m pytest --ignore=tests/control/test_HighContentScreeningGui.py
         working-directory: ./software
+        env:
+          SQUID_PYTEST_HARD_EXIT: "1"
+      - name: Run the GUI test in its own process
+        # Own invocation: the full-application GUI test leaves Qt/thread state
+        # behind that deterministically segfaults later Qt tests (e.g.
+        # test_channel_sequence) when run in the same pytest process.
+        # Step-scoped pyqt5 pin: without it, pytest-qt picks PySide6 for qtbot
+        # while the app code (qtpy) uses PyQt5, and the mixed bindings fail
+        # with a QObject double-init error.
+        run: python3 -m pytest tests/control/test_HighContentScreeningGui.py
+        working-directory: ./software
+        env:
+          QT_API: pyqt5
+          PYTEST_QT_API: pyqt5
+          SQUID_PYTEST_HARD_EXIT: "1"

software/tests/control/conftest.py

@@ -6,6 +6,8 @@
 """
 
 import logging
+import os
+import sys
 from unittest.mock import patch
 
 import pytest
@@ -16,6 +18,27 @@
 logger = logging.getLogger(__name__)
 
 
+def pytest_sessionfinish(session, exitstatus):
+    session.config._squid_exitstatus = int(exitstatus)
+
+
+def pytest_unconfigure(config):
+    """Optionally skip interpreter teardown after the test session.
+
+    Under PyQt5 on Linux, a pytest process that constructed the full HCS GUI
+    segfaults during interpreter shutdown (Qt C++ destructor order conflicts
+    with Python GC) even though every test passed. main_hcs.py sidesteps the
+    same crash with os._exit(); SQUID_PYTEST_HARD_EXIT=1 lets CI's isolated
+    GUI-test invocation do likewise, preserving pytest's exit status.
+    """
+    if os.environ.get("SQUID_PYTEST_HARD_EXIT") == "1":
+        sys.stdout.flush()
+        sys.stderr.flush()
+        # Default 1, not 0: if pytest_sessionfinish never ran (e.g. a
+        # sessionstart failure), an unrecorded status must fail the step.
+        os._exit(getattr(config, "_squid_exitstatus", 1))
+
+
 def _make_tracking_init(original_init, instances_list):
     """Create a wrapper that tracks Microcontroller instances."""