split_body(body, tool) divides every face where the tool meets it and
closes each side with the piece of the tool surface inside the body.
- Patches have outer loops and holes.
- Bands go round a cylinder or another surface of revolution.
- Each side falls apart into its connected parts.
- A body the tool misses comes back whole.
Faces that are B-spline sheets but really planes or circular cylinders
(extruded faces) split as the whole plane or cylinder: the tool is
extended, and the field is exact and cheap.
Tests (volumes): a box split by a plane (2400/3600); a holed plate split
through its hole into two equal halves; a box split by a cylinder's side
into the core (pi*16*30) and the rest; a plane that misses.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL
