split_faces(body, faces, tool) divides the chosen faces where the tool
meets them and leaves the solid unchanged. It handles:
- lines across a face;
- closed lines inside a face (a disc inside a ring);
- lines that run into a hole (the face is divided around it).
Edges the line ends on are cut in every face that uses them. The tool's
zero set is traced on a finely divided triangulation of the face, each
point is placed exactly on the surface by bisection in its parameters,
the ends are placed exactly on the boundary edges, and a cubic is fitted
through the points (a line when they are straight).
Tests: a box top split by a plane (areas 80/120, later booleans still
work); a cylinder side split by a sketch line; a cylinder top split in
ring and disc by a smaller cylinder's face; a plate top split through
its hole into two equal halves; a tool that misses is an error. Volume
and area are unchanged in every case.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL
