DxfImporter now filters ETCH entities (like BEND) since etch marks are
generated from bends during export, not cut geometry. GeometryOptimizer
no longer merges lines/arcs across different layers and preserves layer
and color on merged entities. EntityView draws etch marks directly from
the Bends list so they remain visible without relying on imported ETCH
entities.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
After splitting a drawing with a circular hole, CadConverterForm writes
the split piece to DXF and re-imports it. The circle (decomposed into
two semicircular arcs by DrawingSplitter) was being incorrectly merged
back into a single zero-sweep arc by GeometryOptimizer.TryJoinArcs
during reimport.
Root cause: TryJoinArcs mutated input arc angles in-place and didn't
guard against merging two arcs that together form a full circle. When
arc2 had startAngle=π, endAngle=0 (DXF wrap-around from 360°→0°), the
mutation produced startAngle=-π, and the merge created an arc with
startAngle=π, endAngle=π (zero sweep), losing half the hole.
Fix: use local variables instead of mutating inputs, require arcs to be
adjacent (endpoints touching) rather than just overlapping, and refuse
to merge when the combined sweep would be a full circle.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
