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>
Implements the main drawing splitting algorithm that orchestrates splitting
a Drawing into multiple pieces along split lines using Clipper2 polygon
clipping. After clipping, recovers original arcs by matching clipped edges
back to perimeter entities, stitches in feature edges from ISplitFeature
where polygon edges lie on split lines, and normalizes each piece's origin.
Key fix from plan: filters rapid-layer entities before ShapeProfile
construction so cutouts are properly separated from perimeters.
Includes 7 integration tests covering vertical/horizontal splits, three-way
splits, property copying, origin normalization, cutout assignment, and
grid (cross) splits.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
