apply-theme.ts derives BOTH modes' accent tokens from the stored choice
(ui.theme.accent: preset id or {custom:'#hex'}) and writes them as
<style id="user-theme"> with :root:root + :root:root[data-theme='dark']
blocks — the doubled :root beats tokens.css regardless of document
order, since theme-init.js injects the ui.theme.css cache during <head>
parsing, before the bundle styles. The default preset means NO override
(hand-tuned tokens.css values stay). main.tsx re-derives from the
choice at startup, healing stale caches after app updates.
Settings: accent radiogroup inside the Appearance section (visible
names, color never the only cue) with per-mode preview swatches on
each mode's canonical background, plus a custom color input; i18n
de+en. The second fieldset made bare .settings-fieldset locators
ambiguous — theme specs now scope via input[name] (fence stays).
Tests: apply-theme unit pack, BASE_PALETTE<->tokens.css drift fence in
theme-contrast.test.ts, e2e theme-accent.spec (instant apply, pre-paint
persistence, default removes override, axe smoke with garish yellow in
both modes). ADR 0018 amendment documents the stage-B details.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QRtCnB3uLdQtFmvp9HXcRX
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
