Map a raycast hit on a toolpath chunk mesh — identified by its hit vertex index — back to the IR
segment index (#184, the "click a segment → source line" half). Lines mode has 2 vertices per
segment; tube meshes carry a vertexSegment table (vertex → in-chunk segment). Returns null when
the mesh isn't a pickable chunk or the index is out of range. Pure — testable without a GL context.
Map a raycast hit on a toolpath chunk mesh — identified by its hit vertex index — back to the IR segment index (#184, the "click a segment → source line" half). Lines mode has 2 vertices per segment; tube meshes carry a
vertexSegmenttable (vertex → in-chunk segment). Returns null when the mesh isn't a pickable chunk or the index is out of range. Pure — testable without a GL context.