Dependency-free packages/shared/src/theme.ts: relativeLuminance /
contrastRatio (WCAG 2.1), deriveAccentTokens(hex, mode) keeps hue and
saturation and binary-searches lightness until the accent clears 4.5:1
against the mode's bg, bg-subtle AND surface (a passing hex is kept
verbatim; accent-contrast follows by symmetry). THEME_PRESETS (pond
green = default), BASE_PALETTE as the canonical backgrounds. A sweep
test (36 hues x 3 saturations x 3 lightnesses x both modes) fences the
by-construction guarantee for arbitrary input.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QRtCnB3uLdQtFmvp9HXcRX
