design.md "Intervals" gains the frustum-ball paragraph and the envelope-then-noise
paragraph: how a consumer composes the bound, the short-circuit, and that the warp
lives on the noise only. r1's slab saving paragraph is replaced by r2's printed
numbers per scenario. README names iv_frustum_ball and the envelope composition.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>