fix(terminal): prevent hidden WebGL overlay bleed

src/renderer/src/components/terminal-pane/TerminalPaneOverlayLayer.tsx

@@ -12,6 +12,7 @@ import {
 import TerminalPane from './TerminalPane'
 import { closeTerminalTab } from '../terminal/terminal-tab-actions'
 import { useNativeChatToggleShortcut } from '../native-chat/use-native-chat-toggle-shortcut'
+import { getTerminalOverlayPaintStyle } from './terminal-overlay-paint-style'
 import { shouldDeferParkedPtyExitTabClose } from './terminal-parked-tab-watchers'
 import { useTerminalTabColdParking } from './use-terminal-tab-cold-parking'
 
@@ -187,9 +188,7 @@ const TerminalOverlaySlot = memo(function TerminalOverlaySlot({
             left: `anchor(${anchorName} left)`,
             width: `anchor-size(${anchorName} width)`,
             height: `anchor-size(${anchorName} height)`,
-            display: isVisible || shouldMeasureHiddenStartup ? 'flex' : 'none',
-            opacity: isVisible ? 1 : 0,
-            pointerEvents: isVisible ? 'auto' : 'none'
+            ...getTerminalOverlayPaintStyle(isVisible, shouldMeasureHiddenStartup)
           }
         : anchorName
           ? {
@@ -201,9 +200,7 @@ const TerminalOverlaySlot = memo(function TerminalOverlaySlot({
               left: measuredFallbackRect?.left ?? 0,
               width: measuredFallbackRect?.width ?? '100%',
               height: measuredFallbackRect?.height ?? 'calc(100% - 32px)',
-              display: isVisible || shouldMeasureHiddenStartup ? 'flex' : 'none',
-              opacity: isVisible ? 1 : 0,
-              pointerEvents: isVisible ? 'auto' : 'none'
+              ...getTerminalOverlayPaintStyle(isVisible, shouldMeasureHiddenStartup)
             }
           : {
               position: 'absolute',

src/renderer/src/components/terminal-pane/terminal-overlay-paint-style.test.ts

@@ -0,0 +1,28 @@
+import { describe, expect, it } from 'vitest'
+import { getTerminalOverlayPaintStyle } from './terminal-overlay-paint-style'
+
+describe('getTerminalOverlayPaintStyle', () => {
+  it('keeps a hidden startup terminal measurable without letting it paint', () => {
+    expect(getTerminalOverlayPaintStyle(false, true)).toEqual({
+      display: 'flex',
+      opacity: 0,
+      visibility: 'hidden',
+      pointerEvents: 'none'
+    })
+  })
+
+  it('shows only the active terminal overlay', () => {
+    expect(getTerminalOverlayPaintStyle(true, false)).toEqual({
+      display: 'flex',
+      opacity: 1,
+      visibility: 'visible',
+      pointerEvents: 'auto'
+    })
+    expect(getTerminalOverlayPaintStyle(false, false)).toEqual({
+      display: 'none',
+      opacity: 0,
+      visibility: 'hidden',
+      pointerEvents: 'none'
+    })
+  })
+})

src/renderer/src/components/terminal-pane/terminal-overlay-paint-style.ts

@@ -0,0 +1,21 @@
+import type { CSSProperties } from 'react'
+
+type TerminalOverlayPaintStyle = Pick<
+  CSSProperties,
+  'display' | 'opacity' | 'pointerEvents' | 'visibility'
+>
+
+export function getTerminalOverlayPaintStyle(
+  isVisible: boolean,
+  shouldMeasureHiddenStartup: boolean
+): TerminalOverlayPaintStyle {
+  const shouldLayout = isVisible || shouldMeasureHiddenStartup
+
+  return {
+    display: shouldLayout ? 'flex' : 'none',
+    opacity: isVisible ? 1 : 0,
+    // Why: opacity alone can leak stale WebGL pixels from a measurable hidden xterm on Windows.
+    visibility: isVisible ? 'visible' : 'hidden',
+    pointerEvents: isVisible ? 'auto' : 'none'
+  }
+}