Root cause (evidence: gfx-log) of the opening-CG grey background: a CG drawn with
(alpha=0, color=white) means 'no tint' = fully opaque, but slice-A conflated the
color alpha with object opacity -> the CG rendered transparent. RenderObject now
carries TintStrength separately from Alpha (opacity); resolution keeps textured
objects opaque. Tests updated to the evidence-based semantics.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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