diff --git a/scanslicer/ui_builders.py b/scanslicer/ui_builders.py
index d99d59c..576f8e7 100644
--- a/scanslicer/ui_builders.py
+++ b/scanslicer/ui_builders.py
@@ -4,3 +4,5 @@ from .ui_builders_shared import ScrollbarWheelOnlyScrollArea, icon_from_svg_data
 
 
 # ScanSlicerUiBuilderMixin: class definition for ScanSlicer behavior.
+class ScanSlicerUiBuilderMixin(ScanSlicerUiControlsMixin, ScanSlicerUiPreviewMixin):
+    """Composed UI builder mixin split by panel responsibility."""