2715bc8d0d
Records the volume and material a track is about to enter when a step ends at a geometric boundary, since post-step's physical volume still refers to the volume the step occurred in. Also adds run-sampling-batch.sh to run all run_sampling configs in parallel from isolated directories, avoiding output filename collisions. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>