An edge of one operand crossing the other operand’s surface.
Identified by the edge ALONE, deliberately. The crossed triangle is
not part of the name: a closed surface is triangulated arbitrarily,
so one puncture point can sit on a shared triangle edge and be
reported once per incident triangle. Including the face index would
give that single point two names, and the curve would fragment into
disconnected two-node pieces instead of closing into a loop.
An edge crossing a plane it is NOT parallel to punctures it exactly
once, so the pierced plane completes the name. The plane is identified
by its own geometry rather than by a triangle index: a flat side of a
solid is triangulated arbitrarily, and naming the triangle would give
one puncture two names whenever it lands on a shared triangle edge.
This matters for a through-cut. An edge that enters one side of a slab
and leaves the other punctures the surface TWICE; identifying the node
by the edge alone would collapse both punctures into a single name and
corrupt the curve into degree-3 nodes.