Hollow the evaluated target to walls of thickness, leaving the faces
named by refs open. Refs are serializable node data (the cache key stays
purely structural); they resolve against the materialized target at
evaluation, so an upstream parameter edit re-targets the same faces by
role. Ref order is content-significant.
CSG IR — Constructive Solid Geometry as an Intermediate Representation.
Build a content-addressed DAG of primitives, booleans, and transforms; parameterize via named expression bindings; evaluate against the active kernel with subtree-level cache reuse for incremental parametric edits.