The octave stages of a warp chain over a span, in C#: stretched, shifted, offset octave sums whose
field equals fbm_grad and ridged_grad bit for bit at the identity transform and whose curvature
and fold bounds derive from SNOISE_LIPSCHITZ, SNOISE_HESSIAN and SNOISE_THIRD only (local tier from
the midpoint Hessian's Frobenius norm plus the third-derivative term, capped by the global pin).
SpanStageTests encloses the Hessian norm and the branch departure over seeded spans in both regimes
and checks the gradient against differences and the stretch/axis conventions. README and design.md
state the span, the transform and the bound rules. No shader twin: stage-shaders is part 2.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
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