Patch on v2.0.0 covering the worked-notebook fixes for the
REFERENCE_MESH path (geometry inspect + hierarchical xy zoning +
intervals print), and a regression in _resolve_region_origin where
triangles tagged with the get_indexing_mask -1 sentinel produced
labels like '-1-pack' that crashed int(label.split('-', 1)[0]).
Three regression tests added.

See docs/source/release_notes.md for the full v2.0.1 changeset.