Write omitted z1/z2 whenever both z bounds sat at/outside the sbyte extremes, but Read
reconstructs absent z as exactly z1=-128, z2=127 (depth 255). So any rectangle that tripped
the omit condition without being that sentinel round-tripped to depth 255 — e.g. a
homeRange-style z1=-128/z2=128 (depth 256) silently lost its top z-level on re-serialize.
Omit z only for the exact -128/127 sentinel; write it otherwise.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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