feat: 增强桌面启动失败提示与测试覆盖

backend/cmd/desktop/messagebox_test.go

@@ -47,9 +47,15 @@ func TestMessageBoxW_WindowsOnly_FailureUsesReturnValue(t *testing.T) {
 }
 
 func TestShowError_WindowsBranch(t *testing.T) {
-	withMessageBoxW(t, func(_, _, _, _ uintptr) (uintptr, error) {
-		return 0, syscall.Errno(5)
-	})
+	old := buildPromptChannels
+	buildPromptChannels = func(commandRunner) []promptChannel {
+		return []promptChannel{{
+			name:      "fake-failed-channel",
+			available: func() error { return nil },
+			run:       func(promptRequest) error { return syscall.Errno(5) },
+		}}
+	}
+	t.Cleanup(func() { buildPromptChannels = old })
 
 	defer func() {
 		if recovered := recover(); recovered != nil {
@@ -59,3 +65,42 @@ func TestShowError_WindowsBranch(t *testing.T) {
 
 	showError("测试错误", "这是一条测试错误消息")
 }
+
+func TestMessageBoxW_WindowsOnly_StartupFlags(t *testing.T) {
+	var gotFlags uintptr
+	withMessageBoxW(t, func(_, _, _, flags uintptr) (uintptr, error) {
+		gotFlags = flags
+		return 1, syscall.Errno(0)
+	})
+
+	if err := messageBox("测试标题", "测试消息", messageBoxStartupFlags()); err != nil {
+		t.Fatalf("MessageBoxW 应成功: %v", err)
+	}
+
+	for _, flag := range []uint{mbIconError, mbTaskModal, mbSetForeground, mbTopMost} {
+		if gotFlags&uintptr(flag) == 0 {
+			t.Fatalf("startup flags 缺少 0x%x，实际: 0x%x", flag, gotFlags)
+		}
+	}
+}
+
+func TestWindowsStartupChannelsUseToastBeforeMessageBox(t *testing.T) {
+	runner := &fakeCommandRunner{paths: map[string]bool{"powershell.exe": true}}
+	channels := platformStartupChannels(runner)
+	if len(channels) != 2 {
+		t.Fatalf("Windows 应有 Toast 和 MessageBox 两级通道，实际: %d", len(channels))
+	}
+
+	if channels[0].name != "windows-toast" || channels[1].name != "windows-messagebox" {
+		t.Fatalf("Windows 通道顺序错误: %s, %s", channels[0].name, channels[1].name)
+	}
+	if err := channels[0].available(); err != nil {
+		t.Fatalf("PowerShell 存在时 Toast 通道应可用: %v", err)
+	}
+	if err := channels[0].run(promptRequest{title: "Nex 启动失败", message: "端口被占用"}); err != nil {
+		t.Fatalf("Toast fake runner 应执行成功: %v", err)
+	}
+	if len(runner.calls) != 1 || runner.calls[0].name != "powershell.exe" {
+		t.Fatalf("Toast 应调用 powershell.exe，实际: %#v", runner.calls)
+	}
+}