flowchart TD
    subgraph Layer0["第0层: Reachability / NAT 自检"]
        NAT["AutoNAT / Reachability 状态"] --> Strategy{"评估 NAT 与连接策略"}
    end

    subgraph Layer1["第1层: 智能合约发现"]
        Contract["ContractDiscovery"] --> PeerBook["DiscoveryManager PeerBook"]
    end

    subgraph Layer2["第2层: DHT 发现"]
        DHT["Bootstrapper + DHTDiscoveryAdapter"] --> PeerBook
    end

    subgraph Layer3["第3层: DNS 发现族"]
        DNS["DNS TXT Discovery"] --> PeerBook
        DNSSRV["DNS Seed SRV Discovery"] --> PeerBook
    end

    subgraph Layer4["第4层: mDNS 本地发现"]
        MDNS["mDNS Discovery"] --> PeerBook
    end

    subgraph Layer5["第5层: Seed Nodes 兜底"]
        Seed["SeedDiscovery / 可达性探测"] --> PeerBook
    end

    PeerBook --> ConnMgr["SmartConnectionManager"]
    Strategy --> ConnMgr
    ConnMgr --> PeerID["PeerID Registry"]
    ConnMgr --> Tunnel["Tunnel URL Registry"]

    subgraph ConnectFlow["连接建立与降级升级"]
        PeerID --> P2P["tryP2PConnect -> libp2p NewStream"]
        Tunnel --> HTTP["tryHTTPConnect -> HTTP Tunnel"]
        ConnMgr --> P2P
        ConnMgr --> HTTP
        P2P --> Success["优先使用 P2P SmartConnection"]
        HTTP --> Fallback["P2P 失败时降级 HTTP"]
        Fallback --> Upgrade["autoUpgradeLoop 周期升级回 P2P"]
        Upgrade --> Success
    end

    subgraph HolePunch["Relay / 打洞 / 监控"]
        Success --> Relay["Circuit Relay v2"]
        Relay -.-> DCUtR["DCUtR / Hole Punching"]
        Success --> Monitor["RTT 监控 / 健康检查 / 重连"]
    end