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/probe/src/Monitor.Probe/ProbeApp.cs

@@ -1,13 +1,17 @@
 using Fleet.Core;
 using Fleet.Hosting;
+using System.Text.Json;
 using Fleet.Identity;
+using Fleet.Link;
+using Fleet.Rpc;
 using Monitor.Measurement;
+using Monitor.Protocol;
 
 namespace Monitor.Probe;
 
 /// <summary>
-/// Probe 的组装点：Agent 列表 → 每个 Agent 一个连接（认证、重连、角色）。没有全局状态，测试可以在同一进程里启动多个。
-/// 列表变化时只调和连接：新增的建立，移除的断开，地址或证书指纹变化的重建，其余不受影响。
+/// Probe 的组装点：到面板的长连接（身份、Agent 列表、状态）+ 每个 Agent 一个测量连接（认证、重连、角色）。没有全局状态，测试可以在同一进程里启动多个。
+/// Agent 列表变化时只调和连接：新增的建立，移除的断开，地址或证书指纹变化的重建，其余不受影响。
 /// </summary>
 public sealed class ProbeApp : IDisposable
 {
@@ -17,16 +21,39 @@ public sealed class ProbeApp : IDisposable
     private readonly Dictionary<string, Running> _connections = [];
     private readonly SemaphoreSlim _changed = new(0);
     private readonly INodeLog _log;
+    private readonly FleetLink _link;
 
     public ProbeApp(ProbeFile file, string configDirectory, TimeProvider time, INodeLog log)
     {
         _log = log;
-        var directory = new AgentDirectory(new ConfigStore(configDirectory), configDirectory, file, log);
+        var directory = new AgentDirectory(new ConfigStore(configDirectory), configDirectory, log);
         NodeIdentity identity = NodeIdentity.FromPkcs8(Convert.FromBase64String(file.PrivateKey));
         _env = new ConnectionEnv(identity, file.ProbeId, file.Limits, directory, new MonoClock(time), time, log);
         directory.Changed += () => _changed.Release();
+
+        var options = new FleetLinkOptions
+        {
+            Server = new Uri(file.Server),
+            Identity = identity,
+            NodeId = new NodeId(file.ProbeId),
+            NodeVersion = Version,
+            Capabilities = [MonitorCapabilities.Base],
+            HelloMeta = () => JsonSerializer.SerializeToElement(new ProbeHelloMeta { Platform = PlatformDetector.Detect() }, MonitorJsonContext.Default.ProbeHelloMeta),
+        };
+        var list = new StateHandler<ProbeAgentList>(
+            ProbeAgentList.StateType,
+            MonitorJsonContext.Default.ProbeAgentList,
+            (version, doc, _) =>
+            {
+                directory.Apply(doc);
+                return ValueTask.FromResult(new StateSyncResult { AppliedVersion = version });
+            });
+        _link = new FleetLink(options, new RpcRouter<LinkContext>(), [list], new Outbox(1 << 20), time, log);
     }
 
+    /// <summary>到面板的连接（测试和状态查看用）。</summary>
+    public FleetLink Link => _link;
+
     public AgentDirectory Directory => _env.Directory;
 
     /// <summary>某个 Agent 的会话是否已经建立（测试和状态查看用）。</summary>
@@ -50,9 +77,10 @@ public sealed class ProbeApp : IDisposable
     {
         if (_env.Directory.Agents.Count == 0)
         {
-            _log.Warn("no agents known yet: probe.json has an empty bootstrap list");
+            _log.Info("no agents known yet, waiting for the panel to send the list");
         }
 
+        Task link = _link.RunAsync(ct);
         try
         {
             while (!ct.IsCancellationRequested)
@@ -68,6 +96,7 @@ public sealed class ProbeApp : IDisposable
         finally
         {
             await ReconcileAsync([], CancellationToken.None);
+            await Task.WhenAny(link, Task.Delay(TimeSpan.FromSeconds(5), CancellationToken.None));
         }
     }
 
@@ -77,7 +106,7 @@ public sealed class ProbeApp : IDisposable
         _changed.Dispose();
     }
 
-    private async Task ReconcileAsync(IReadOnlyList<BootstrapAgent> agents, CancellationToken ct)
+    private async Task ReconcileAsync(IReadOnlyList<KnownAgent> agents, CancellationToken ct)
     {
         var wanted = agents.ToDictionary(a => a.AgentId);
         var stopped = new List<Running>();
@@ -85,7 +114,7 @@ public sealed class ProbeApp : IDisposable
         {
             foreach ((string id, Running running) in _connections.ToList())
             {
-                if (!wanted.TryGetValue(id, out BootstrapAgent? endpoint) || !AgentDirectory.Equal(endpoint, running.Connection.Endpoint))
+                if (!wanted.TryGetValue(id, out KnownAgent? endpoint) || !AgentDirectory.Equal(endpoint, running.Connection.Endpoint))
                 {
                     stopped.Add(running);
                     _connections.Remove(id);
@@ -105,7 +134,7 @@ public sealed class ProbeApp : IDisposable
 
         lock (_connections)
         {
-            foreach ((string id, BootstrapAgent endpoint) in wanted)
+            foreach ((string id, KnownAgent endpoint) in wanted)
             {
                 if (!_connections.ContainsKey(id))
                 {