feat: add periodic server stats and account connection heartbeat publishing

src/NATS.Server/Events/InternalEventSystem.cs

@@ -85,6 +85,50 @@ public sealed class InternalEventSystem : IAsyncDisposable
         _sendLoop = Task.Run(() => InternalSendLoopAsync(ct), ct);
         _receiveLoop = Task.Run(() => InternalReceiveLoopAsync(_receiveQueue, ct), ct);
         _receiveLoopPings = Task.Run(() => InternalReceiveLoopAsync(_receiveQueuePings, ct), ct);
+
+        // Periodic stats publish every 10 seconds
+        _ = Task.Run(async () =>
+        {
+            using var timer = new PeriodicTimer(TimeSpan.FromSeconds(10));
+            while (await timer.WaitForNextTickAsync(ct))
+            {
+                PublishServerStats();
+            }
+        }, ct);
+    }
+
+    /// <summary>
+    /// Publishes a $SYS.SERVER.{id}.STATSZ message with current server statistics.
+    /// Maps to Go's sendStatsz in events.go.
+    /// Can be called manually for testing or is invoked periodically by the stats timer.
+    /// </summary>
+    public void PublishServerStats()
+    {
+        if (_server == null) return;
+
+        var subject = string.Format(EventSubjects.ServerStats, _server.ServerId);
+        var process = System.Diagnostics.Process.GetCurrentProcess();
+
+        var statsMsg = new ServerStatsMsg
+        {
+            Server = _server.BuildEventServerInfo(),
+            Stats = new ServerStatsData
+            {
+                Start = _server.StartTime,
+                Mem = process.WorkingSet64,
+                Cores = Environment.ProcessorCount,
+                Connections = _server.ClientCount,
+                TotalConnections = Interlocked.Read(ref _server.Stats.TotalConnections),
+                Subscriptions = SystemAccount.SubList.Count,
+                InMsgs = Interlocked.Read(ref _server.Stats.InMsgs),
+                OutMsgs = Interlocked.Read(ref _server.Stats.OutMsgs),
+                InBytes = Interlocked.Read(ref _server.Stats.InBytes),
+                OutBytes = Interlocked.Read(ref _server.Stats.OutBytes),
+                SlowConsumers = Interlocked.Read(ref _server.Stats.SlowConsumers),
+            },
+        };
+
+        Enqueue(new PublishMessage { Subject = subject, Body = statsMsg });
     }
 
     /// <summary>

tests/NATS.Server.Tests/SystemEventsTests.cs

@@ -74,6 +74,28 @@ public class SystemEventsTests
         await server.ShutdownAsync();
     }
 
+    [Fact]
+    public async Task Server_publishes_statsz_periodically()
+    {
+        using var server = CreateTestServer();
+        _ = server.StartAsync(CancellationToken.None);
+        await server.WaitForReadyAsync();
+
+        var received = new TaskCompletionSource<string>();
+        server.EventSystem!.SysSubscribe("$SYS.SERVER.*.STATSZ", (sub, client, acc, subject, reply, hdr, msg) =>
+        {
+            received.TrySetResult(subject);
+        });
+
+        // Trigger a manual stats publish (don't wait 10s)
+        server.EventSystem!.PublishServerStats();
+
+        var result = await received.Task.WaitAsync(TimeSpan.FromSeconds(5));
+        result.ShouldContain(".STATSZ");
+
+        await server.ShutdownAsync();
+    }
+
     [Fact]
     public async Task Server_publishes_shutdown_event()
     {