test(gpu): pin the win32-only fallback invariant the macOS Graphite fix relies on (#10646)

Co-authored-by: Orca <help@stably.ai>

src/main/startup/configure-process.ts

@@ -264,6 +264,8 @@ export function enableMainProcessGpuFeatures(): void {
 
   if (process.platform === 'darwin') {
     // Why: Graphite can strand corrupt Metal tiles after idle; Ganesh preserves GPU compositing without the stale surface.
+    // Reached on every macOS launch only because GPU fallback skips this function and is win32-only; if fallback ever
+    // reaches macOS this must move out of this path or Macs silently lose the fix.
     app.commandLine.appendSwitch('disable-skia-graphite')
   }
 

src/main/startup/gpu-fallback-marker.test.ts

@@ -79,6 +79,21 @@ describe('gpu-fallback-marker', () => {
     expect(existsSync(join(userDataPath, GPU_FALLBACK_MARKER_FILE))).toBe(false)
   })
 
+  // Why: enableMainProcessGpuFeatures() is skipped while GPU fallback is active, and that function
+  // carries the macOS disable-skia-graphite fix. A marker that survived on darwin would silently
+  // strip the fix from the Macs it targets, so pin the platform gate for darwin specifically.
+  it('clears an active marker on macOS so the Graphite fix is never skipped', () => {
+    writeGpuFallbackMarker(userDataPath, { engagedAt: 1, crashesInWindow: 4 }, environment)
+
+    expect(
+      readActiveGpuFallbackMarker(userDataPath, {
+        ...environment,
+        platform: 'darwin'
+      })
+    ).toBeNull()
+    expect(existsSync(join(userDataPath, GPU_FALLBACK_MARKER_FILE))).toBe(false)
+  })
+
   it('clears a corrupt or wrong-version marker', () => {
     writeFileSync(join(userDataPath, GPU_FALLBACK_MARKER_FILE), '{ not json')
     expect(readGpuFallbackMarker(userDataPath)).toBeNull()