feat!: probes connect to the backend directly

A probe now links to the backend like an agent (probe.json carries the
server address). The backend sends the agent list as desired state and the
probe reports its platform and build in its own hello. The agent no longer
relays the list or the probe platform. Existing probes must be re-created.

backend/agent/src/Monitor.Agent/AgentApp.cs

@@ -209,14 +209,6 @@ public sealed class AgentApp : IDisposable
                 async (_, request, _) => Result<TestRunResult>.Ok(new TestRunResult { Accepted = await _hub.DisconnectAsync(request.ProbeId.Value) }));
         }
 
-        if (Allow(MonitorMethods.ProbeAgentsChanged))
-        {
-            router.OnNotify(
-                MonitorMethods.ProbeAgentsChanged,
-                MonitorJsonContext.Default.ProbeAgentsResult,
-                (_, list, _) => _hub.RelayAgentsAsync(list));
-        }
-
         var options = new FleetLinkOptions
         {
             Server = new Uri(_config.Fleet.Server),

backend/agent/src/Monitor.Agent/DataPlane/Registries.cs

@@ -64,9 +64,6 @@ public sealed class ProbeSession : DataSession
 
     public long ConnectedAtUtcMs { get; init; }
 
-    /// <summary>Probe 自报的系统和架构（随列表同步一起来，只用于展示）；还没报过就是 null。</summary>
-    public PlatformInfo? Platform { get; set; }
-
     public RpcSession<PeerContext>? Rpc { get; set; }
 
     /// <summary>最近一次认证通过的 UDP 包的源地址（Agent 把单向数据发往这里）。</summary>

backend/agent/src/Monitor.Agent/Peer/PeerHub.cs

@@ -57,18 +57,6 @@ public sealed class BackendUplink
         await SafeAsync(() => session.NotifyAsync(MonitorMethods.TestStatus, parameters, MonitorJsonContext.Default.TestStatusParams, CancellationToken.None));
     }
 
-    /// <summary>代 Probe 向 Backend 取 Agent 列表（Probe 不认识 Backend）。链路断开时返回 fleet_node_offline。</summary>
-    public async ValueTask<Result<ProbeAgentsResult>> RequestProbeAgentsAsync(ProbeAgentsParams request, CancellationToken ct)
-    {
-        RpcSession<LinkContext>? session = _link?.CurrentSession;
-        if (session is null)
-        {
-            return Result<ProbeAgentsResult>.Fail(FleetErrors.NodeOffline, "the agent has no link to the backend");
-        }
-
-        return await session.RequestAsync(MonitorMethods.ProbeAgents, request, MonitorJsonContext.Default.ProbeAgentsParams, MonitorJsonContext.Default.ProbeAgentsResult, ct);
-    }
-
     private static async ValueTask SafeAsync(Func<ValueTask> send)
     {
         try
@@ -104,7 +92,7 @@ public sealed class PeerHub
 
     public PeerHub(SessionRegistry sessions, MonoClock clock, ChunkAssembler chunks, TaskManager tasks, BackendUplink uplink, TimeProvider time, INodeLog log)
     {
-        _router = BuildRouter(uplink);
+        _router = BuildRouter();
         _sessions = sessions;
         _clock = clock;
         _chunks = chunks;
@@ -220,7 +208,7 @@ public sealed class PeerHub
     /// <summary>当前连着的 Probe（心跳和 Backend 重连之后的补报都用它）。</summary>
     public IReadOnlyList<ConnectedProbe> ConnectedProbes() => [.. _sessions.All.Select(Describe)];
 
-    private static ConnectedProbe Describe(ProbeSession p) => new() { Id = new ProbeId(p.ProbeId), Version = p.Version, Remote = p.RemoteAddress, SinceUtcMs = p.ConnectedAtUtcMs, Platform = p.Platform };
+    private static ConnectedProbe Describe(ProbeSession p) => new() { Id = new ProbeId(p.ProbeId), Version = p.Version, Remote = p.RemoteAddress, SinceUtcMs = p.ConnectedAtUtcMs };
 
     public IReadOnlyList<string> ConnectedProbeIds() => [.. _sessions.All.Select(p => p.ProbeId)];
 
@@ -252,27 +240,6 @@ public sealed class PeerHub
         }
     }
 
-    /// <summary>Backend 的 Agent 列表变化时转交给所有 Probe（Probe 据此调整它连接的 Agent）。</summary>
-    public async ValueTask RelayAgentsAsync(ProbeAgentsResult list)
-    {
-        foreach (ProbeSession probe in _sessions.All)
-        {
-            if (probe.Rpc is not { } rpc)
-            {
-                continue;
-            }
-
-            try
-            {
-                await rpc.NotifyAsync(MonitorMethods.ProbeAgentsChanged, list, MonitorJsonContext.Default.ProbeAgentsResult, CancellationToken.None);
-            }
-            catch (Exception ex) when (ex is ObjectDisposedException or InvalidOperationException or IOException)
-            {
-                // 会话刚好结束
-            }
-        }
-    }
-
     private async ValueTask PushAsync(ProbeSession probe, LineTaskSet set, CancellationToken ct)
     {
         if (probe.Rpc is null)
@@ -300,21 +267,8 @@ public sealed class PeerHub
         }
     }
 
-    private static RpcRouter<PeerContext> BuildRouter(BackendUplink uplink) =>
+    private static RpcRouter<PeerContext> BuildRouter() =>
         new RpcRouter<PeerContext>()
-            .On(
-                MonitorMethods.ProbeAgents,
-                MonitorJsonContext.Default.ProbeAgentsParams,
-                MonitorJsonContext.Default.ProbeAgentsResult,
-                (context, request, ct) =>
-                {
-                    if (request.Platform is { } platform)
-                    {
-                        context.Session.Platform = platform;
-                    }
-
-                    return uplink.RequestProbeAgentsAsync(request, ct);
-                })
             .On(
                 MonitorMethods.Clock,
                 MonitorJsonContext.Default.ClockParams,