some fixes

python_app/gui/main.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+from contextlib import suppress
 import os
 from pathlib import Path
 import signal
@@ -63,7 +64,12 @@ def main() -> int:
         _install_unix_signal_handlers(app, window)
     else:
         window.showMaximized()
-    return app.exec()
+    exit_code = app.exec()
+    # Release hardware, SHM readers and child processes before exiting so that a
+    # systemd restart (after a headless fatal exit) starts from a clean slate.
+    with suppress(Exception):
+        window.close()
+    return exit_code
 
 
 if __name__ == "__main__":