StarletBootstrapProbe: fail on a Dolphin alert instead of opening a dialog

With no handler registered, Dolphin shows an alert in a modal MessageBox
on Windows, and the probe waits until someone closes it. A run that hits
an alert then looks like a hang (StarOS EXP-001). The probe now writes the
alert to stderr and exits at once with status 3.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

Tools/StarletBootstrapProbe/StarletBootstrapProbe.cpp

@@ -1,12 +1,14 @@
 // Copyright 2026 Dolphin Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
+#include <cstdlib>
 #include <fstream>
 #include <iostream>
 #include <string>
 #include <string_view>
 #include <vector>
 
+#include "Common/MsgHandler.h"
 #include "Core/Core.h"
 #include "Core/HW/WII_IPC.h"
 #include "Core/IOS/Starlet/ARMCore.h"
@@ -25,6 +27,18 @@ enum class ExpectedOutcome
   Phase2
 };
 
+// Exit status of a run stopped by a Dolphin alert (1: failed expectation, 2: usage).
+constexpr int ALERT_EXIT_STATUS = 3;
+
+// Dolphin's default handler shows an alert in a modal MessageBox on Windows, which blocks the
+// probe until someone closes it. Report the alert on stderr and fail the run at once instead.
+bool FailOnAlert(const char* caption, const char* text, bool, Common::MsgType)
+{
+  std::cout.flush();
+  std::cerr << "Dolphin alert (" << caption << "): " << text << std::endl;
+  std::_Exit(ALERT_EXIT_STATUS);
+}
+
 bool Run(const std::string& path, bool jit, ExpectedOutcome expected)
 {
   std::ifstream file(path, std::ios::binary | std::ios::ate);
@@ -132,6 +146,7 @@ bool Run(const std::string& path, bool jit, ExpectedOutcome expected)
 
 int main(int argc, char** argv)
 {
+  Common::RegisterMsgAlertHandler(FailOnAlert);
   if (argc < 2 || argc > 4)
   {
     std::cerr << "Usage: StarletBootstrapProbe <ELF> [--jit] "