add script to check if VR headset is connected

Assets/Scripts/StartupHeadsetCheck.cs

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+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+using UnityEngine.XR;
+using UnityEngine.XR.Management;
+
+public class StartupHeadsetCheck : MonoBehaviour
+{
+#if UNITY_STANDALONE_WIN && !UNITY_EDITOR
+    [DllImport("user32.dll", CharSet = CharSet.Unicode)]
+    private static extern int MessageBox(System.IntPtr hWnd, string text, string caption, uint type);
+#endif
+
+    private IEnumerator Start()
+    {
+        // Let OpenXR/XR Management initialize.
+        yield return null;
+        yield return null;
+        yield return null;
+
+        if (!IsOpenXRRunning())
+        {
+            ShowWindowsErrorMessage();
+            Application.Quit();
+        }
+    }
+
+    private bool IsOpenXRRunning()
+    {
+        XRManagerSettings xrManager = XRGeneralSettings.Instance?.Manager;
+
+        if (xrManager == null || xrManager.activeLoader == null)
+        {
+            return false;
+        }
+
+        var displays = new List<XRDisplaySubsystem>();
+        SubsystemManager.GetSubsystems(displays);
+
+        foreach (XRDisplaySubsystem display in displays)
+        {
+            if (display.running)
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    private void ShowWindowsErrorMessage()
+    {
+#if UNITY_STANDALONE_WIN && !UNITY_EDITOR
+        MessageBox(
+            System.IntPtr.Zero,
+            "No VR headset detected.\n\n" +
+            "Please connect your headset and make sure your OpenXR runtime is active.\n\n" +
+            "SteamVR headset: start SteamVR.\n" +
+            "Meta Quest Link/Air Link: start Meta Quest Link.\n" +
+            "WMR headset: start Mixed Reality Portal.\n\n" +
+            "Then restart the game.",
+            "VR Headset Not Detected",
+            0x10 // MB_ICONERROR
+        );
+#else
+        Debug.LogError("No VR headset detected.");
+#endif
+    }
+}

Assets/Scripts/StartupHeadsetCheck.cs.meta

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+fileFormatVersion: 2
+guid: 3b9f3cb88b161274baaeee6f00477851