The shared ensureContrast shipped the TUI's fine 0.05×20 ladder, which
changed --dt-primary-solid for 7 of 15 desktop presets (nous #3b6acb →
#3f70d8, cyberpunk #00661a → #008021, slate #505457 → #6f7377) while the PR
body said no preset VALUE changed. The ladder is now the desktop's original
algorithm exactly — pole by luminance < 0.5, accumulating 0.2 steps up to
1.0001, re-mixed from the source colour — with `step` as a parameter. The
only pre-refactor TUI caller (ColorChain.ensureContrast) passes 0.05, so
the terminal palette is byte-identical too.
Test: apps/desktop context.test.tsx iterates every builtin preset × mode,
paints it through ThemeProvider and asserts --dt-primary-solid equals the
value a reference copy of the old desktop algorithm computes. Sabotage
(default step 0.05): 11/30 rows fail. Docs: the SDK table now lists
contrastRatio as `number | null` under sRGB measures, not OKLCH.