Concatenate per-level LoadedMeshData into the revealed prefix.
Face indices are LOCAL to each level's own vertex array (the writer's
split_mesh_by_faces renumbers every part), so they are offset-adjusted by
the cumulative vertex count — the same value-adding loop
concatenateLinesData uses for segment indices, and the reason faces cannot
go through concatRequiredField, which .set()s verbatim. Using the
helper would produce a plausible-looking garbage surface rather than a crash.
Concatenate per-level
LoadedMeshDatainto the revealed prefix.Face indices are LOCAL to each level's own vertex array (the writer's
split_mesh_by_facesrenumbers every part), so they are offset-adjusted by the cumulative vertex count — the same value-adding loopconcatenateLinesDatauses for segment indices, and the reason faces cannot go through concatRequiredField, which.set()s verbatim. Using the helper would produce a plausible-looking garbage surface rather than a crash.