On cad-agent excavator project, fusing nine nearly coincident swept solids in one call gave an invalid shape. The invalid tool then cut nothing from the boom, and only a range-of-motion collision check caught it, 14.7 cm3 of overlap. A cone meeting a pin hole raised Null TopoDS_Shape until the tool was nudged 0.01 mm, and a sub-micron split vertex made a valid solid fail the watertight export.