Fix: Modern Terminal blank under SYSTEM; precise reason in info list

server/2015Remote/TerminalModuleLoader.h

@@ -136,6 +136,35 @@ inline bool IsTerminalModuleLoaded()
     return g_hTerminalModule != nullptr;
 }
 
+// Check if current process is running as LocalSystem (S-1-5-18).
+// 用途：WebView2 / msedgewebview2.exe 子进程拒绝在 SYSTEM token 下渲染（Microsoft
+// 官方限制），此时 Modern Terminal 会打开但页面空白，需要回退到经典终端。
+// 结果缓存，因为进程 token 在生命周期内不会变。
+inline bool IsRunningAsSystem()
+{
+    static int cached = -1;
+    if (cached >= 0) return cached == 1;
+
+    bool isSystem = false;
+    HANDLE hToken = nullptr;
+    if (OpenProcessToken(GetCurrentProcess(), TOKEN_QUERY, &hToken)) {
+        BYTE buf[256] = {};
+        DWORD len = 0;
+        if (GetTokenInformation(hToken, TokenUser, buf, sizeof(buf), &len)) {
+            SID_IDENTIFIER_AUTHORITY ntAuth = SECURITY_NT_AUTHORITY;
+            PSID pSystemSid = nullptr;
+            if (AllocateAndInitializeSid(&ntAuth, 1, SECURITY_LOCAL_SYSTEM_RID,
+                                         0, 0, 0, 0, 0, 0, 0, &pSystemSid)) {
+                isSystem = EqualSid(((TOKEN_USER*)buf)->User.Sid, pSystemSid) != FALSE;
+                FreeSid(pSystemSid);
+            }
+        }
+        CloseHandle(hToken);
+    }
+    cached = isSystem ? 1 : 0;
+    return isSystem;
+}
+
 // Check if WebView2 Runtime is installed (cached)
 inline bool IsWebView2Available()
 {