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DXF files can contain degenerate arcs where start angle equals end angle (zero sweep), often left as construction artifacts by CAD software. These create spurious shapes in ShapeBuilder — e.g. SULLYS-033.dxf showed 5 loops instead of 4 (3 cutouts + perimeter). Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>