The merged meshes for assembleTraceScene: the plan and one tree per group, from any builder.
Readonly
plan.groups[g].geometry built by any builder (tinybvh, GPU H-PLOC, LBVH): records as the builder wrote them.
plan.groups[g].geometry
From mergeStaticGeometry, over the same instances (with the same transforms).
The merged meshes for assembleTraceScene: the plan and one tree per group, from any builder.