修复二开 agent 流量增量丢失: 基线改上报确认后推进并落盘持久化

- xray 新增快照/确认接口 GetTrafficSnapshot/CommitTrafficSnapshot/
  RestoreTrafficBaseline, 与面板 GetTraffic 的 StatsLastValues 完全隔离
- agent 改走快照: 仅主控 HTTP 200 后才推进基线, 失败轮增量由累计
  计数做差在下轮自动补齐; 已确认基线原子落盘, agent 重启恢复续差
- 核心重启计数归零的从零规则保留; Onlines 仍每轮新鲜采集直报
- 新增 11 个测试覆盖断网恢复/连续失败补齐/重启恢复/计数归零/
  面板语义隔离, xray 与 agent 两包全绿

main.go

@@ -11,6 +11,7 @@ import (
 	_ "net/http/pprof"
 	"os"
 	"os/signal"
+	"path/filepath"
 	"syscall"
 	_ "unsafe"
 
@@ -84,6 +85,12 @@ func runAgent(args []string) {
 		log.Fatalf("Failed to load agent config from %s: %v", configPath, err)
 	}
 
+	// The acknowledged traffic baseline persists next to the agent config
+	// (its state home, e.g. /etc/x-ui), unless the config names a path.
+	if cfg.BaselinePath == "" {
+		cfg.BaselinePath = filepath.Join(filepath.Dir(configPath), "agent-traffic-baseline.json")
+	}
+
 	// Initialize logger
 	logger.InitLogger(logging.INFO)
 	log.Printf("Starting 3x-ui agent (node: %s)", cfg.NodeName)