feat: declare every protocol method's direction and enforce it in the router; add the zero-trust design [CI]

Methods, roles and binary channels are declared in one table per plane (node and peer). RpcRouter checks direction, kind and role when handlers are registered, when messages arrive (fleet_protocol_violation, disconnect after repeated violations) and before sending. NodeConnection is split by responsibility.

backend/fleet/src/Fleet.Server.Link/NodeConnection.State.cs

@@ -0,0 +1,123 @@
+using System.Text.Json;
+using Fleet.Core;
+using Fleet.Rpc;
+
+namespace Fleet.Server;
+
+/// <summary>状态：期望状态推送、在线状态、节点事件。</summary>
+internal sealed partial class NodeConnection
+{
+    public void SignalStateChanged() => _stateSignal.Writer.TryWrite(true);
+
+
+    private async Task StatePushLoopAsync(CancellationToken ct)
+    {
+        while (await _stateSignal.Reader.WaitToReadAsync(ct))
+        {
+            _stateSignal.Reader.TryRead(out _);
+            bool complete = await PushStateAsync(ct);
+            if (!complete)
+            {
+                await Task.Delay(s_statePushRetry, _host.Time, ct);
+                SignalStateChanged();
+            }
+        }
+    }
+
+    private async Task<bool> PushStateAsync(CancellationToken ct)
+    {
+        NodeRecord? fresh = await _host.Store.GetNodeAsync(_node!.Id, ct);
+        if (fresh is null)
+        {
+            return true;
+        }
+
+        _node = fresh with { NodeVersion = _node.NodeVersion ?? fresh.NodeVersion };
+        if (fresh.Status == NodeStatus.Disabled)
+        {
+            await RevokeAsync("disabled", ct);
+            return true;
+        }
+
+        if (fresh.Status != NodeStatus.Active || !_helloDone)
+        {
+            // pending 不下发状态；还没有 hello 的连接等 hello 之后再推送。
+            return true;
+        }
+
+        bool complete = true;
+        foreach (IStateProvider provider in _host.StateProviders)
+        {
+            StateDocument? document = await provider.GetAsync(_node, ct);
+            if (document is null || (_lastPushedVersion.TryGetValue(provider.Type, out long last) && last == document.Version))
+            {
+                continue;
+            }
+
+            Result<JsonElement> raw = await RequestAsync(
+                FleetMethods.StateSync,
+                JsonSerializer.SerializeToElement(
+                    new StateSyncParams { Type = provider.Type, Version = document.Version, Doc = document.Doc },
+                    FleetRpcContext.Default.StateSyncParams),
+                ct);
+            if (!raw.TryGet(out JsonElement value, out FleetError? error))
+            {
+                FleetLog.StatePushFailed(_host.Logger, _node.Id.Value, provider.Type, error.Code.Value);
+                complete = false;
+                continue;
+            }
+
+            StateSyncResult? result = null;
+            try
+            {
+                result = value.Deserialize(FleetRpcContext.Default.StateSyncResult);
+            }
+            catch (JsonException)
+            {
+                // 按缺失处理
+            }
+
+            if (result is null)
+            {
+                complete = false;
+                continue;
+            }
+
+            _lastPushedVersion[provider.Type] = document.Version;
+            await provider.OnAppliedAsync(_node, document.Version, result, ct);
+        }
+
+        return complete;
+    }
+
+
+    private async Task UpdatePresenceAsync(bool online, CancellationToken ct)
+    {
+        Interlocked.Exchange(ref _lastPresenceTicks, _host.Time.GetTimestamp());
+        await _host.Store.UpdatePresenceAsync(
+            _node!.Id,
+            new Presence(online, _host.Time.GetUtcNow().ToUnixTimeMilliseconds(), _session?.NodeVersion, _session?.Capabilities ?? [], _session?.HelloMetaJson),
+            ct);
+    }
+
+    private async Task FireAsync(NodeEventKind kind, CancellationToken ct, HelloParams? hello = null, JsonElement? extra = null)
+    {
+        var nodeEvent = new NodeEvent(kind, _node!, _host.Time.GetUtcNow().ToUnixTimeMilliseconds(), hello, extra);
+        foreach (INodeEventSink sink in _host.Sinks)
+        {
+            try
+            {
+                await sink.OnEventAsync(nodeEvent, ct);
+            }
+            catch (OperationCanceledException) when (ct.IsCancellationRequested)
+            {
+                throw;
+            }
+            catch (Exception ex)
+            {
+                // 产品的事件处理失败不能影响连接。
+                FleetLog.SinkFailed(_host.Logger, ex, kind.ToString(), _node!.Id.Value);
+            }
+        }
+    }
+}