some fixes

python_app/gui/control_button.py

@@ -86,12 +86,23 @@ class ControlButtonWatcher(QObject):
 
     def start(self) -> None:
         """Open the GPIO line and begin watching for presses on a background thread."""
-        self._line.open()
-        self._stop_read_fd, self._stop_write_fd = os.pipe()
-        self._thread = threading.Thread(
-            target=self._run, name="control-button-watcher", daemon=True
-        )
-        self._thread.start()
+        # Guard against double-start: a second start would leak the first line/pipe/thread.
+        if self._thread is not None:
+            return
+        try:
+            self._line.open()
+            self._stop_read_fd, self._stop_write_fd = os.pipe()
+            self._thread = threading.Thread(
+                target=self._run, name="control-button-watcher", daemon=True
+            )
+            self._thread.start()
+        except Exception:
+            # Release any line/pipe fds opened before the failure so nothing leaks
+            # and no orphaned thread survives a partial start.
+            self._thread = None
+            self._close_stop_pipe()
+            self._line.close()
+            raise
 
     def stop(self) -> None:
         """Signal the watcher thread to exit and release the GPIO line and pipe."""