fix(terminal): floor ANSI colors to 3:1 contrast on light themes

[slowdini]

Problem

Several terminal ANSI colors are illegible on the light-mode backgrounds (#FFF8F5 pastel-light, #FAF6FA neon-light). Terminal colors were pulled straight from the palette with no readability adjustment — the same values that work as sparse, often-bold editor syntax tokens fail as terminal text. Measured WCAG contrast against #FFF8F5: yellow ~1.6:1, cyan ~1.7:1, green ~2.1:1, blue/magenta ~2.2:1, red ~2.9:1 — all below a 3:1 floor.

A second, directional bug compounded it: brightHex/bright/bright8 always lightened the bright variants. Lightening helps on a dark background but pushes colors toward a light one, so bright green/yellow/cyan were the faintest of all (~1.4:1) — the pale prompt/TUI text users saw.

Dark themes were unaffected, which matches what users observed in the wild.

Fix

• generator/colorUtils.ts — add relativeLuminance, contrastRatio, and ensureContrast. ensureContrast nudges only a color's lightness (preserving hue/saturation) just enough to reach a minimum contrast against the background, darkening on a light bg and lightening on a dark one. It's a no-op when the color already passes.
• All four terminal targets (wezterm.ts, vscode.ts, zed.ts, neovim.ts) — apply a 3:1 contrast floor to the chromatic ANSI text colors (normal + bright). "Bright" is now direction-aware (lighter on dark, darker on light) before flooring. Structural black/white slots are left untouched.

3:1 was chosen to fix legibility while preserving the synthwave/vaporwave palette as much as possible; the nudge is minimal, so colors that already pass keep their vividness.

Result

Every chromatic terminal color (normal + bright) now clears 3:1 on the light backgrounds:

pastel-light  bg=#FFF8F5
ansi  : red 3.01  grn 3.00  yel 3.01  blu 3.02  mag 3.01  cyn 3.02
bright: red 3.72  grn 3.00  yel 3.01  blu 4.41  mag 3.33  cyn 3.02
neon-light    bg=#FAF6FA
ansi  : red 3.89  grn 3.00  yel 3.02  blu 5.03  mag 4.15  cyn 3.01
bright: red 5.35  grn 3.30  yel 3.01  blu 7.41  mag 5.85  cyn 3.16

Dark themes are byte-for-byte unchanged — the floor is a no-op where colors already pass, so the dark wezterm/vscode output files weren't touched.

Tests

20 new tests (RED→GREEN), covering the WCAG utilities and asserting per-target that light-mode chromatic colors meet 3:1 while dark-mode values stay pinned to their existing hexes.

• bun test → 111 pass, 0 fail
• bun run check (biome + tsc --noEmit) → clean

Out of scope

The Starship powerline prompt is a separate code path (hardcodes the dark palette, draws fg:crust on colored segments) and isn't driven by the ANSI mapping. Plain ANSI-colored shell text benefits from this fix; making the Starship segments themselves mode-aware is a follow-up.

🤖 Generated with Claude Code