fix: improve terminal contrast in light themes (Tango Light + xterm minimumContrastRatio) (#5986)

* fix: darken Builtin Tango Light ANSI colors for readability

Nine ANSI colors had contrast ratios below 3:1 against the white
background, making CLI output unreadable in light mode. Darkened
to readable Tango shades while keeping the warm palette identity.

Co-Authored-By: Claude <noreply@anthropic.com>

* fix: enable xterm minimumContrastRatio and add light theme tests

xterm.js minimumContrastRatio (4.5) auto-adjusts low-contrast ANSI
foreground colors at render time — a safety net for all themes,
including custom imports. Added test coverage for this option and
for the Tango Light ANSI color contrast assertions.

Co-Authored-By: Claude <noreply@anthropic.com>

* chore: trigger CI re-run

---------

Co-authored-by: zhangqinzhong <vhudsongit@gmail.com>
Co-authored-by: Claude <noreply@anthropic.com>

src/renderer/src/lib/pane-manager/pane-lifecycle.test.ts

@@ -83,6 +83,10 @@ describe('buildDefaultTerminalOptions', () => {
     expect(buildDefaultTerminalOptions().scrollbar?.width).toBe(7)
   })
 
+  it('enables xterm contrast correction for low-contrast CLI colors', () => {
+    expect(buildDefaultTerminalOptions().minimumContrastRatio).toBe(4.5)
+  })
+
   it('only uses inactive outline for block cursors', () => {
     expect(resolveTerminalCursorInactiveStyle('block')).toBe('outline')
     expect(resolveTerminalCursorInactiveStyle('bar')).toBe('bar')

src/renderer/src/lib/pane-manager/pane-terminal-options.ts

@@ -27,6 +27,9 @@ export function buildDefaultTerminalOptions(): ITerminalOptions {
     fontWeightBold: '500',
     scrollback: 10000,
     allowTransparency: false,
+    // Why: agent CLIs sometimes render body text with ANSI white/bright-white
+    // on light themes; xterm can keep those cells readable across renderers.
+    minimumContrastRatio: 4.5,
     // Why: on macOS, non-US layouts rely on Option to compose characters like @ and €.
     macOptionIsMeta: false,
     macOptionClickForcesSelection: true,

src/renderer/src/lib/terminal-theme.test.ts

@@ -261,6 +261,26 @@ describe('default dark terminal theme selection contrast', () => {
   })
 })
 
+describe('default light terminal theme ANSI contrast', () => {
+  it('keeps CLI body/header ANSI colors readable on the terminal background', () => {
+    const theme = getBuiltinTheme(DEFAULT_TERMINAL_THEME_LIGHT)
+
+    expect(theme, `${DEFAULT_TERMINAL_THEME_LIGHT} should exist`).not.toBeNull()
+    if (!theme?.background) {
+      throw new Error(`${DEFAULT_TERMINAL_THEME_LIGHT} is missing a background color`)
+    }
+
+    for (const key of ['cyan', 'white', 'brightCyan', 'brightWhite'] as const) {
+      const color = theme[key]
+      expect(color, `${DEFAULT_TERMINAL_THEME_LIGHT}.${key} should be defined`).toBeDefined()
+      if (!color) {
+        throw new Error(`${DEFAULT_TERMINAL_THEME_LIGHT}.${key} is missing`)
+      }
+      expect(contrastRatio(color, theme.background)).toBeGreaterThanOrEqual(4.5)
+    }
+  })
+})
+
 describe('isTerminalBackgroundLight', () => {
   it('classifies common terminal background color formats by luminance', () => {
     const split = vi.spyOn(String.prototype, 'split')

src/renderer/src/lib/terminal-themes/defaults.ts

@@ -38,18 +38,20 @@ export const DEFAULT_TERMINAL_THEMES: TerminalThemeMap = {
     black: '#2e3436',
     red: '#cc0000',
     green: '#4e9a06',
-    yellow: '#c4a000',
+    // Why: Claude-style previews use ANSI accent colors for readable text,
+    // so the light theme cannot keep Tango's near-white legacy values.
+    yellow: '#8e7700',
     blue: '#3465a4',
     magenta: '#75507b',
-    cyan: '#06989a',
-    white: '#d3d7cf',
+    cyan: '#05727e',
+    white: '#6a6a6a',
     brightBlack: '#555753',
     brightRed: '#ef2929',
-    brightGreen: '#8ae234',
-    brightYellow: '#fce94f',
-    brightBlue: '#729fcf',
+    brightGreen: '#1b7a1b',
+    brightYellow: '#6d5a00',
+    brightBlue: '#204a87',
     brightMagenta: '#ad7fa8',
-    brightCyan: '#34e2e2',
-    brightWhite: '#eeeeec'
+    brightCyan: '#034b50',
+    brightWhite: '#3d3d3d'
   }
 }