Deterministic placement heuristic (Best-Area-Fit with tiebreak on
shorter remaining short side). Power-of-2-rounded output bounds for
GPU friendliness. Oversize hard-fails with packed-area diagnostic.
Test bounds corrected: guillotine split fills tiles left-to-right,
so 3x 32x32 tiles produce boundsW=128 (not 64 as the plan draft had).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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