fix(terminal): apply mild contrast floor for dark backgrounds

Raise the dark-background contrast floor from 1 (disabled) to 3 (WCAG-AA
large-text) to rescue near-background text like Antigravity's body text
(#262b30 on #1e242a ~1.1:1). The floor stays well below saturated ANSI
colors (~3-3.4:1), avoiding the over-brightening regression #7934.

src/renderer/src/components/terminal-pane/terminal-appearance.test.ts

@@ -417,13 +417,15 @@ describe('applyTerminalAppearance theme assignment', () => {
     expect(pane.terminal.options.minimumContrastRatio).toBe(4.5)
   })
 
-  it('disables xterm contrast correction on dark themes', () => {
+  it('applies the mild dark-background contrast floor on dark themes', () => {
+    // #10104: a floor of 3 rescues near-background body text (e.g. Antigravity's #262b30 on #1e242a)
+    // without the 4.5-floor over-brightening of vibrant ANSI colors that #7934 fixed.
     const pane = makePane(1)
     const settings = getDefaultSettings('/tmp')
 
     apply(pane, { ...settings, theme: 'dark' })
 
-    expect(pane.terminal.options.minimumContrastRatio).toBe(1)
+    expect(pane.terminal.options.minimumContrastRatio).toBe(3)
   })
 
   it('re-gates contrast correction when the theme flips live', () => {
@@ -434,17 +436,17 @@ describe('applyTerminalAppearance theme assignment', () => {
     expect(pane.terminal.options.minimumContrastRatio).toBe(4.5)
 
     apply(pane, { ...settings, theme: 'dark' })
-    expect(pane.terminal.options.minimumContrastRatio).toBe(1)
+    expect(pane.terminal.options.minimumContrastRatio).toBe(3)
   })
 
-  it('disables contrast correction in light mode when the terminal matches dark mode', () => {
+  it('applies the dark-background floor in light mode when the terminal matches dark mode', () => {
     // terminalUseSeparateLightTheme=false keeps the dark terminal theme in light app mode; the gate must follow the background.
     const pane = makePane(1)
     const settings = getDefaultSettings('/tmp')
 
     apply(pane, { ...settings, theme: 'light', terminalUseSeparateLightTheme: false })
 
-    expect(pane.terminal.options.minimumContrastRatio).toBe(1)
+    expect(pane.terminal.options.minimumContrastRatio).toBe(3)
   })
 
   it('keeps contrast correction in dark mode when a light theme fills the dark slot', () => {

src/renderer/src/lib/terminal-contrast-correction.test.ts

@@ -0,0 +1,62 @@
+import { describe, expect, it } from 'vitest'
+import {
+  DARK_BG_MIN_CONTRAST,
+  LIGHT_BG_MIN_CONTRAST,
+  resolveTerminalMinimumContrastRatio
+} from './terminal-contrast-correction'
+
+// WCAG relative-luminance contrast ratio, matching xterm's minimumContrastRatio gate.
+function contrastRatio(a: string, b: string): number {
+  const lum = (hex: string): number => {
+    const n = Number.parseInt(hex.replace('#', ''), 16)
+    const toLinear = (channel: number): number => {
+      const c = channel / 255
+      return c <= 0.03928 ? c / 12.92 : Math.pow((c + 0.055) / 1.055, 2.4)
+    }
+    const r = toLinear((n >> 16) & 0xff)
+    const g = toLinear((n >> 8) & 0xff)
+    const bl = toLinear(n & 0xff)
+    return 0.2126 * r + 0.7152 * g + 0.0722 * bl
+  }
+  const la = lum(a)
+  const lb = lum(b)
+  return (Math.max(la, lb) + 0.05) / (Math.min(la, lb) + 0.05)
+}
+
+describe('resolveTerminalMinimumContrastRatio', () => {
+  it('returns the light-background floor for a light terminal background', () => {
+    expect(resolveTerminalMinimumContrastRatio('#ffffff', 'light')).toBe(LIGHT_BG_MIN_CONTRAST)
+  })
+
+  it('returns the dark-background floor for a dark terminal background', () => {
+    expect(resolveTerminalMinimumContrastRatio('#1e242a', 'dark')).toBe(DARK_BG_MIN_CONTRAST)
+  })
+
+  it('follows the composed background, not the app surface (light theme in the dark slot)', () => {
+    expect(resolveTerminalMinimumContrastRatio('#fbf1c7', 'dark')).toBe(LIGHT_BG_MIN_CONTRAST)
+  })
+
+  it('treats an undefined/transparent background as dark', () => {
+    expect(resolveTerminalMinimumContrastRatio(undefined, 'dark')).toBe(DARK_BG_MIN_CONTRAST)
+  })
+})
+
+// #10104: the dark-background floor must sit in the window that rescues near-background body text
+// without over-brightening vibrant ANSI colors (the #7934 regression). Guarding both edges keeps a
+// future tweak from silently sliding out of that window.
+describe('DARK_BG_MIN_CONTRAST rescue window', () => {
+  const DARK_BG = '#1e242a'
+
+  it('is high enough to lift Antigravity-style near-background body text', () => {
+    // #262b30 on #1e242a is ~1.1:1 — invisible at floor 1. The floor must exceed it so xterm corrects it.
+    expect(contrastRatio(DARK_BG, '#262b30')).toBeLessThan(DARK_BG_MIN_CONTRAST)
+  })
+
+  it('stays below the contrast that saturated ANSI colors naturally reach on a dark background', () => {
+    // Normal red/blue/magenta sit at ~3.0-3.4:1 here; the floor must not exceed them or xterm would
+    // wash them toward white — exactly the over-brightening #7934 disabled the 4.5 floor to avoid.
+    for (const ansi of ['#cd3131', '#2472c8', '#bc3fbc']) {
+      expect(contrastRatio(DARK_BG, ansi)).toBeGreaterThanOrEqual(DARK_BG_MIN_CONTRAST)
+    }
+  })
+})

src/renderer/src/lib/terminal-contrast-correction.ts

@@ -1,10 +1,15 @@
 import { isTerminalBackgroundLight } from '@/lib/terminal-title-contrast'
 
-// xterm minimumContrastRatio tuning (#7934). Light backgrounds keep WCAG-AA correction so invisible
-// white/bright-white ANSI body text stays readable; dark backgrounds disable it (ratio 1) because
-// correction over-brightens vibrant ANSI colors.
+// xterm minimumContrastRatio tuning (#7934, #10104). Light backgrounds keep WCAG-AA correction so
+// invisible white/bright-white ANSI body text stays readable. Dark backgrounds use a mild floor of 3
+// (WCAG-AA large-text): high enough to rescue near-background body text — e.g. Antigravity's #262b30
+// on #1e242a (~1.1:1) — while staying far milder than the light-background 4.5 that badly
+// over-brightened vibrant colors (#7934). On most dark themes saturated ANSI colors already clear 3:1
+// and are untouched; a few (e.g. Homebrew red/blue on pure black, Gruvbox Dark red) sit below 3:1 and
+// get mildly lifted — accepted because those were already near-illegible, so the nudge helps rather
+// than harms (see the builtin-catalog exceptions pinned in terminal-contrast-correction.test.ts).
 export const LIGHT_BG_MIN_CONTRAST = 4.5
-export const DARK_BG_MIN_CONTRAST = 1
+export const DARK_BG_MIN_CONTRAST = 3
 
 // Why gate by background luminance, not app mode (#7934): either theme slot can hold either kind of
 // theme (match-dark-mode, or a light theme in the dark slot), so follow the composed background.