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

build.ps1

@@ -43,6 +43,18 @@ foreach ($pattern in $msBuildPaths) {
     }
 }
 
+# 兜底：默认路径找不到（例如 VS 装在 D 盘）时，用 vswhere 反查。
+# vswhere.exe 由 VS Installer 维护，固定在 %ProgramFiles(x86)% 下，与 VS 本体盘符无关。
+if (-not $msBuild) {
+    $vswhere = "${env:ProgramFiles(x86)}\Microsoft Visual Studio\Installer\vswhere.exe"
+    if (Test-Path $vswhere) {
+        $found = & $vswhere -latest -products * -requires Microsoft.Component.MSBuild `
+                            -find "MSBuild\**\Bin\MSBuild.exe" 2>$null |
+                 Select-Object -First 1
+        if ($found) { $msBuild = $found }
+    }
+}
+
 if (-not $msBuild) {
     Write-Host "ERROR: MSBuild not found." -ForegroundColor Red
     Write-Host ""

server/2015Remote/2015RemoteDlg.cpp

@@ -5618,12 +5618,23 @@ VOID CMy2015RemoteDlg::MessageHandle(CONTEXT_OBJECT* ContextObject)
         break;
     }
     case TOKEN_TERMINAL_START: { // Linux PTY 终端 (WebView2 + xterm.js)
-        // 检查 WebView2 和 DLL，都满足则使用现代终端，否则退化到经典终端
-        if (IsWebView2Available() && LoadTerminalModule()) {
+        // 三个前置条件，缺任何一个都回退到经典终端，并把原因贴到信息列表。
+        // SYSTEM 场景：WebView2 不支持 LocalSystem token，会出现"窗口能弹但页面空白"，
+        // 显式拦截一次，避免用户误以为是 bug。
+        const char* fallbackReason = nullptr;
+        if (IsRunningAsSystem()) {
+            fallbackReason = "Modern Terminal does not support SYSTEM, falling back to classic";
+        } else if (!IsWebView2Available()) {
+            fallbackReason = "WebView2 Runtime not installed, falling back to classic";
+        } else if (!LoadTerminalModule()) {
+            fallbackReason = "TerminalModule.dll load failed, falling back to classic";
+        }
+
+        if (fallbackReason == nullptr) {
             g_2015RemoteDlg->SendMessage(WM_OPENTERMINALDIALOG, 0, (LPARAM)ContextObject);
         } else {
-            g_2015RemoteDlg->PostMessageA(WM_SHOWMESSAGE, 
-                (WPARAM)new CharMsg("To use Modern Terminal - WebView2 and TerminalModule.dll are required"), NULL);
+            g_2015RemoteDlg->PostMessageA(WM_SHOWMESSAGE,
+                (WPARAM)new CharMsg(fallbackReason), NULL);
             g_2015RemoteDlg->SendMessage(WM_OPENSHELLDIALOG, 0, (LPARAM)ContextObject);
         }
         break;

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()
 {