[CultElementId(nameof(Member))] declares an id derived from that member's
invariant text, never random, so content-addressed elements keep encoding to the
same bytes. CultMeshCdnChunkRef derives its id from Offset; PackArtifact sets
it, the Rust pack_content writes it, and the committed content vectors are
re-cut once so both runtimes carry it. Engine tests drive Problems and Assign
directly (InternalsVisibleTo the Caching tests).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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