fix(agent): systemctl 模式 Status 补充失败原因(LastError)

enable=false 时走 NewSystemCtlController，其 Status() 在服务未运行时
只返回 Running:false 无原因。现通过 systemctl show 获取
ActiveState/SubState/Result/ExecMainStatus/NRestarts，
给出可读提示: '启动失败(退出码 X, 已重启 N 次)' 或 '未运行(systemctl: x/y)'

edge/agent/internal/procctl/systemctl.go

@@ -29,24 +29,24 @@ func (s *SystemCtlController) Status() (Status, error) {
 	// 检查服务是否运行
 	cmd := exec.Command("systemctl", "is-active", "--quiet", s.serviceName)
 	err := cmd.Run()
-	
+
 	if err != nil {
-		// 服务未运行
-		return Status{Running: false}, nil
+		// 服务未运行：附带失败原因（退出码/重启次数），供 UI 展示
+		return Status{Running: false, LastError: s.failureHint()}, nil
 	}
-	
+
 	// 获取 PID
 	pidCmd := exec.Command("systemctl", "show", "--property=MainPID", "--value", s.serviceName)
 	out, err := pidCmd.Output()
 	if err != nil {
 		return Status{Running: true}, nil // 运行但无法获取 PID
 	}
-	
+
 	pid, _ := strconv.Atoi(strings.TrimSpace(string(out)))
 	if pid <= 0 {
 		return Status{Running: true}, nil
 	}
-	
+
 	return Status{
 		Running:    true,
 		Pid:        pid,
@@ -54,6 +54,36 @@ func (s *SystemCtlController) Status() (Status, error) {
 	}, nil
 }
 
+// failureHint 查询 systemctl 状态，给出服务未运行的可用原因（如启动失败/退出码）
+func (s *SystemCtlController) failureHint() string {
+	out, err := exec.Command("systemctl", "show", "--property=ActiveState,SubState,Result,ExecMainStatus,NRestarts", s.serviceName).Output()
+	if err != nil {
+		return fmt.Sprintf("媒体服务未运行 (%s)", s.serviceName)
+	}
+	props := map[string]string{}
+	for _, line := range strings.Split(strings.TrimSpace(string(out)), "\n") {
+		if idx := strings.IndexByte(line, '='); idx > 0 {
+			props[strings.TrimSpace(line[:idx])] = strings.TrimSpace(line[idx+1:])
+		}
+	}
+	switch {
+	case props["SubState"] == "failed" || props["Result"] == "exit-code":
+		code := props["ExecMainStatus"]
+		if code == "" {
+			code = "?"
+		}
+		restarts := props["NRestarts"]
+		if restarts == "" {
+			restarts = "0"
+		}
+		return fmt.Sprintf("媒体服务启动失败（退出码 %s，已重启 %s 次）", code, restarts)
+	case props["ActiveState"] != "" || props["SubState"] != "":
+		return fmt.Sprintf("媒体服务未运行（systemctl: %s/%s）", props["ActiveState"], props["SubState"])
+	default:
+		return fmt.Sprintf("媒体服务未运行 (%s)", s.serviceName)
+	}
+}
+
 func (s *SystemCtlController) Version() (string, error) {
 	// 从 systemctl 获取 ExecStart 路径，再调用 --version
 	// Output format: { path=/path/to/binary ; argv[]=... }