Structured Exception Handling in WinUI apps

Describe the bug

The main WinUI thread interferes with Structured Exception Handling.

A top-level unhandled exception filter doesn't get called, no matter whether it's set as early as possible (on startup in App constructor or DllMain), or as late as possible (immediately before triggering a test crash).

LONG WINAPI HandleGlobalException(EXCEPTION_POINTERS* exceptionInfo) {
    OutputDebugString(L"HandleGlobalException\n");
    return EXCEPTION_CONTINUE_SEARCH;
}

void TriggerCrash()
{
    volatile int* pInt = 0x00000000;
    *pInt = 20;
}

void winrt::BlankApp::implementation::MainWindow::OnButtonClick(winrt::Windows::Foundation::IInspectable const& sender, winrt::Microsoft::UI::Xaml::RoutedEventArgs const& e)
{
    LPTOP_LEVEL_EXCEPTION_FILTER lpOldFilter = SetUnhandledExceptionFilter(&HandleGlobalException);

    TriggerCrash(); // HandleGlobalException does not get called

    SetUnhandledExceptionFilter(lpOldFilter);
}

Steps to reproduce the bug

1. Create a new Visual Studio C++ project: WinUI Blank App
2. Install a top-level Unhandled Exception Filter
3. Start without debugging
4. Trigger a crash

Expected behavior

The Unhandled Exception Filter gets called.

Screenshots

No response

NuGet package version

WinUI 3 - Windows App SDK 1.7.3: 1.7.250606001

Windows version

Windows 11 (24H2): Build 26100

Additional context

Originates from:

• https://github.com/getsentry/sentry-native/issues/644

Additional notes:

• Manually wrapping TriggerCrash() with __try and __except does work, but does not help a generic crash handler much :)

  __try {
      TriggerCrash(); // HandleLocalException does get called
  }
  __except (HandleLocalException(GetExceptionInformation())) {
  }
  

• The filter does get called if a crash is triggered from a worker thread:

  std::thread([]() {
      LPTOP_LEVEL_EXCEPTION_FILTER lpOldFilter = SetUnhandledExceptionFilter(&HandleGlobalException);
  
      TriggerCrash(); // HandleGlobalException does get called
  
      SetUnhandledExceptionFilter(lpOldFilter);
  }).join();
  

Reproduce the issue in a new Visual Studio C++ WinUI Blank App using the startup and button-click locations described, then compare the main UI thread with the worker-thread example. Check how WinUI 3 handles the top-level unhandled exception filter and confirm that the expected filter callback occurs for a main-thread crash without requiring a local __try/__except wrapper.