Instancer3D
GPU GpuAttach an InstanceArray3D bundle to a scene fragment for instanced draws.
Takes a scene input (VividSceneFragment carrying mesh + material) plus an
instances input (InstanceArray3D carrying per-instance transforms +
colours) and emits a scene fragment whose instance_buffer / instance_count
are populated. MeshDraw / Render3D issue a single instanced draw from that
buffer.
Layout generation is no longer done inside this operator — use InstanceGrid
for Grid / Circle / Line / Grid3D, InstanceNoise for jitter, and
InstancesFromLanes to migrate per-attribute lane-array signal sources into
the bundle. See docs/plans/2d-pipeline-redesign.md for the canonical
recipe and Phase B history.