Gate WebGL context retention to Windows

Context re-creation is ~5ms on macOS/Linux GL, so retention buys no
perceptible switch latency there while still costing hidden-pane GPU
memory and a new lifecycle to reason about. Only Windows (ANGLE ->
D3D11, 100-500ms per pane) retains; other platforms keep the
long-proven dispose-on-hide behavior.

src/renderer/src/lib/pane-manager/pane-rendering-control.ts

@@ -7,7 +7,11 @@ import {
   markComplexScriptOutput,
   resetWebglTextureAtlas
 } from './pane-webgl-renderer'
-import { retainSuspendedWebglPane, unretainWebglPane } from './pane-webgl-context-retention'
+import {
+  retainSuspendedWebglPane,
+  shouldRetainSuspendedWebglContexts,
+  unretainWebglPane
+} from './pane-webgl-context-retention'
 import { reattachWebglIfNeeded } from './pane-webgl-reattach'
 
 export function setPaneGpuRenderingState(
@@ -44,12 +48,17 @@ export function markPaneComplexScriptOutput(
 }
 
 export function suspendPaneRendering(panes: Iterable<ManagedPaneInternal>): void {
+  const retainContexts = shouldRetainSuspendedWebglContexts()
   for (const pane of panes) {
-    // Why: deferred blocks NEW context creation while hidden; live contexts
-    // are retained (not disposed) so the return switch repaints instantly
-    // instead of paying ANGLE context re-creation. The LRU cap bounds how
-    // many hidden panes may keep one.
+    // Why: deferred blocks NEW context creation while hidden; on Windows,
+    // live contexts are retained (not disposed) so the return switch repaints
+    // instantly instead of paying ANGLE context re-creation. The LRU cap
+    // bounds how many hidden panes may keep one.
     pane.webglAttachmentDeferred = true
+    if (!retainContexts) {
+      disposeWebgl(pane)
+      continue
+    }
     for (const evicted of retainSuspendedWebglPane(pane)) {
       disposeWebgl(evicted)
     }

src/renderer/src/lib/pane-manager/pane-webgl-context-retention.test.ts

@@ -66,16 +66,21 @@ function fireContextLoss(pane: ManagedPaneInternal): void {
   addon._onContextLoss.fire()
 }
 
-describe('terminal WebGL context retention across hide/show', () => {
+function stubCommonGlobals(userAgent: string): void {
+  vi.stubGlobal('navigator', { userAgent })
+  vi.stubGlobal('requestAnimationFrame', (callback: FrameRequestCallback) => {
+    callback(16)
+    return 1
+  })
+  vi.stubGlobal('cancelAnimationFrame', vi.fn())
+}
+
+describe('terminal WebGL context retention across hide/show (Windows)', () => {
   beforeEach(() => {
     resetTerminalWebglSuggestion()
     clearRetainedWebglPanes()
     vi.spyOn(console, 'warn').mockImplementation(() => {})
-    vi.stubGlobal('requestAnimationFrame', (callback: FrameRequestCallback) => {
-      callback(16)
-      return 1
-    })
-    vi.stubGlobal('cancelAnimationFrame', vi.fn())
+    stubCommonGlobals('Mozilla/5.0 (Windows NT 10.0; Win64; x64)')
   })
 
   afterEach(() => {
@@ -193,3 +198,38 @@ describe('terminal WebGL context retention across hide/show', () => {
     expect(pane.webglAddon).not.toBeNull()
   })
 })
+
+describe('terminal WebGL context retention is Windows-only', () => {
+  beforeEach(() => {
+    resetTerminalWebglSuggestion()
+    clearRetainedWebglPanes()
+    vi.spyOn(console, 'warn').mockImplementation(() => {})
+    stubCommonGlobals('Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7)')
+  })
+
+  afterEach(() => {
+    clearRetainedWebglPanes()
+    vi.unstubAllGlobals()
+    vi.restoreAllMocks()
+  })
+
+  it('keeps the dispose-on-hide behavior off Windows', () => {
+    const pane = createAttachedPane()
+
+    suspendPaneRendering([pane])
+
+    expect(pane.webglAttachmentDeferred).toBe(true)
+    expect(pane.webglAddon).toBeNull()
+    expect(retainedWebglPaneCount()).toBe(0)
+  })
+
+  it('re-attaches on resume off Windows as before', () => {
+    const pane = createAttachedPane()
+    suspendPaneRendering([pane])
+
+    resumePaneRendering([pane])
+
+    expect(pane.webglAddon).not.toBeNull()
+    expect(pane.terminal.loadAddon).toHaveBeenCalledTimes(2)
+  })
+})

src/renderer/src/lib/pane-manager/pane-webgl-context-retention.ts

@@ -1,3 +1,4 @@
+import { getRendererAppPlatform } from '@/lib/renderer-app-platform'
 import type { ManagedPaneInternal } from './pane-manager-types'
 
 // Why: workspace switches used to dispose every hidden pane's WebGL context
@@ -7,6 +8,13 @@ import type { ManagedPaneInternal } from './pane-manager-types'
 // this LRU cap only bounds hidden-pane GPU memory.
 export const RETAINED_WEBGL_PANE_CAP = 16
 
+/** Windows-only: context re-creation is cheap on macOS/Linux GL, so hidden
+ *  panes there keep the long-proven dispose-on-hide behavior instead of
+ *  paying retention's GPU-memory cost for no perceptible switch latency win. */
+export function shouldRetainSuspendedWebglContexts(): boolean {
+  return getRendererAppPlatform() === 'win32'
+}
+
 // Insertion order doubles as LRU order: re-retaining deletes + re-adds.
 const retainedPanes = new Set<ManagedPaneInternal>()