Replace the synthetic step-9-at-opacity alpha ramp with a real compositing inverse: each --scale-X-aN is the translucent color that, painted over the scale's background (white for light scales, black for dark, by step-1 luminance), reproduces the opaque solid step N (Radix model). Computed in render-css.ts for ANY theme (base + custom), so alpha is consistent-by-construction with the solid scale and cannot drift. alphaScales opt-in still wins verbatim; non-hex solids fall back to the legacy color-mix ramp. Verified: --scale-purple-a9 = rgb(92 0 173 / 0.6941) over white = #8e4ec6.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
dev