fix(csaxs): aerotech plot stops following once its window is closed

A closed plot made every redraw fail with a warning for each line of each
scan. The first failure now stops following the scans (unsubscribes) with one
message to reopen the plot with csaxs.aerotech.plot().

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01M8zoDzDfsCTY2o5bT3J7Wv

csaxs_bec/bec_ipython_client/plugins/cSAXS/aerotech.py

@@ -231,6 +231,14 @@ class _LivePositions:
                     lines = list(self._lines)
                 try:
                     _draw(self.curves, lines)
-                except Exception as exc:  # window closed, GUI restarted
-                    logger.warning(f"csaxs.aerotech.plot: redraw failed: {exc}")
+                except Exception as exc:  # window or plot closed, GUI restarted
+                    # stop following instead of failing on every line of every scan
+                    logger.warning(
+                        f"csaxs.aerotech.plot: the plot is gone ({exc}); stopped following"
+                        " the scans. Call csaxs.aerotech.plot() to open it again."
+                    )
+                    self.stop()
+                    if self.parent._live is self:
+                        self.parent._live = None
+                    return
                 self._stop.wait(self.parent.REDRAW_INTERVAL)

tests/tests_bec_ipython_client/test_cSAXS_aerotech.py

@@ -145,3 +145,24 @@ def test_live_ignores_other_scans():
     tool._live._on_scan_status(SimpleNamespace(value=status))
     assert client.connector.register.call_count == registered
     tool.stop_plot()
+
+
+def test_live_stops_once_when_the_plot_is_closed():
+    client = _client()
+    waveform = _waveform(client)
+    forward, backward = mock.MagicMock(), mock.MagicMock()
+    forward.set_data.side_effect = RuntimeError("widget has been deleted")
+    waveform.plot.side_effect = [forward, backward]
+    client.history.__getitem__.side_effect = IndexError
+    tool = cSAXSAerotech(client)
+    with mock.patch(
+        "csaxs_bec.bec_ipython_client.plugins.cSAXS.aerotech.logger"
+    ) as logger:
+        tool.plot()
+        live = tool._live
+        live._set_lines(_snake(n_lines=2))
+        live._worker.join(timeout=3)
+    assert not live._worker.is_alive()
+    assert tool._live is None
+    assert logger.warning.call_count == 1
+    client.connector.unregister.assert_called()