Mesh extraction (4 tests): quad output, double-sided via Stippling.Both,
double-sided via SidesType=Clockwise (AC's NoNeg-clear convention),
NoPos-only emission. Pins GfxObjMesh.Build's behavior.
Setup flatten (5 tests): identity (no frames), Default frame, Resting
beats Default, motion override beats Resting, DefaultScale per part.
Pins SetupMesh.Flatten's placement-frame fallback chain.
These run BEFORE substitution per N.1/N.3 pattern — they prove
equivalence, not test the substitution.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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