feat: 增强桌面启动失败提示与测试覆盖

backend/cmd/desktop/startup_error_test.go

@@ -0,0 +1,40 @@
+package main
+
+import (
+	"errors"
+	"strings"
+	"testing"
+)
+
+func TestStartupErrorContainsPhaseAndCause(t *testing.T) {
+	cause := errors.New("底层失败")
+	err := newStartupError(phaseDatabase, "数据库初始化失败", cause)
+
+	if err.Phase() != "database" {
+		t.Fatalf("phase = %q, want database", err.Phase())
+	}
+	if !errors.Is(err, cause) {
+		t.Fatal("startupError 应保留底层 cause")
+	}
+	if !strings.Contains(err.Error(), "database") {
+		t.Fatalf("错误字符串应包含 phase，实际: %s", err.Error())
+	}
+}
+
+func TestStartupErrorRedactsSensitiveUserMessage(t *testing.T) {
+	message := "数据库初始化失败: nex:secret@tcp(localhost:3306)/nex password=secret api_key=sk-test"
+	err := newStartupError(phaseDatabase, message, errors.New("cause password=secret api_key=sk-test"))
+	userMessage := err.UserMessage()
+
+	for _, secret := range []string{"secret", "sk-test"} {
+		if strings.Contains(userMessage, secret) {
+			t.Fatalf("用户提示不应包含敏感信息 %q，实际: %s", secret, userMessage)
+		}
+		if strings.Contains(err.Error(), secret) {
+			t.Fatalf("日志错误字符串不应包含敏感信息 %q，实际: %s", secret, err.Error())
+		}
+	}
+	if !strings.Contains(userMessage, "<redacted>") {
+		t.Fatalf("用户提示应包含脱敏占位符，实际: %s", userMessage)
+	}
+}