improved logging

python_app/gui/preprocess_dialog.py

@@ -462,7 +462,12 @@ class PreprocessDialog(QDialog):
         )
 
     def _ensure_preview_plots(self) -> bool:
-        """Create the amplitude+phase plot pair lazily on first successful capture."""
+        """Lazily create the amplitude+phase plot pair and report whether it exists.
+
+        Returns True once both plots are available. If construction fails (e.g. an
+        incompatible PyQtGraph/PyQt6 build), marks the preview permanently
+        unavailable so later captures fall back to the placeholder without retrying.
+        """
         if self._amplitude_plot is not None and self._phase_plot is not None:
             return True
         if self._preview_plot_unavailable:
@@ -474,6 +479,8 @@ class PreprocessDialog(QDialog):
             amplitude_plot = self._build_preview_axis("Magnitude", "dB")
             phase_plot = self._build_preview_axis("Phase", "deg")
         except Exception:
+            # Some PyQtGraph/PyQt6 combinations cannot build a PlotWidget here;
+            # latch the failure so we show the text placeholder instead of retrying.
             self._preview_plot_unavailable = True
             return False