fix #6682: avoid applying styles directly to geometry when inherited from material

When duplicating elements, skip assign_body_styles if the element's
constituent materials already have style representations. This prevents
creating redundant IfcStyledItem entities on the geometry when styles
should be inherited from the material definition.

src/bonsai/bonsai/core/root.py

@@ -18,6 +18,7 @@
 
 from __future__ import annotations
 from typing import TYPE_CHECKING, Optional
+import ifcopenshell.util.element
 
 if TYPE_CHECKING:
     import bpy
@@ -53,11 +54,32 @@ def copy_class(
             geometry.copy_data_links(data, copied_entities)
             geometry.change_object_data(obj, data, is_global=True)
             geometry.rename_object(data, geometry.get_representation_name(ifc.get_entity(data)))
-        root.assign_body_styles(new, obj)
+        # Only assign styles if element doesn't get them from material
+        if not _has_material_styles(ifc, new):
+            root.assign_body_styles(new, obj)
     collector.assign(obj)
     return new
 
 
+def _has_material_styles(ifc: type[tool.Ifc], element: ifcopenshell.entity_instance) -> bool:
+    """Check if element has styles defined through its material.
+    
+    Returns True if any constituent material has a style representation,
+    which means styles should NOT be applied directly to the geometry.
+    """
+    materials = ifcopenshell.util.element.get_materials(element)
+    
+    if not materials:
+        return False
+    
+    # Check if any of the constituent materials have styles
+    for material in materials:
+        if hasattr(material, 'HasRepresentation') and material.HasRepresentation:
+            return True
+    
+    return False
+
+
 def assign_class(
     ifc: type[tool.Ifc],
     collector: type[tool.Collector],