feat: add MaxSubs enforcement, delivery-time deny filtering, auto-unsub cleanup

src/NATS.Server/Auth/ClientPermissions.cs

@@ -45,8 +45,18 @@ public sealed class ClientPermissions : IDisposable
     {
         if (_subscribe == null)
             return true;
+        if (!_subscribe.IsAllowed(subject))
+            return false;
+        if (queue != null && _subscribe.IsDenied(queue))
+            return false;
+        return true;
+    }
 
-        return _subscribe.IsAllowed(subject);
+    public bool IsDeliveryAllowed(string subject)
+    {
+        if (_subscribe == null)
+            return true;
+        return _subscribe.IsDeliveryAllowed(subject);
     }
 
     public void Dispose()
@@ -117,6 +127,21 @@ public sealed class PermissionSet : IDisposable
         return allowed;
     }
 
+    public bool IsDenied(string subject)
+    {
+        if (_deny == null) return false;
+        var result = _deny.Match(subject);
+        return result.PlainSubs.Length > 0 || result.QueueSubs.Length > 0;
+    }
+
+    public bool IsDeliveryAllowed(string subject)
+    {
+        if (_deny == null)
+            return true;
+        var result = _deny.Match(subject);
+        return result.PlainSubs.Length == 0 && result.QueueSubs.Length == 0;
+    }
+
     public void Dispose()
     {
         _allow?.Dispose();

src/NATS.Server/ClientClosedReason.cs

@@ -23,6 +23,7 @@ public enum ClientClosedReason
     ServerShutdown,
     MsgHeaderViolation,
     NoRespondersRequiresHeaders,
+    AuthenticationExpired,
 }
 
 public static class ClientClosedReasonExtensions
@@ -46,6 +47,7 @@ public static class ClientClosedReasonExtensions
         ClientClosedReason.ServerShutdown => "Server Shutdown",
         ClientClosedReason.MsgHeaderViolation => "Message Header Violation",
         ClientClosedReason.NoRespondersRequiresHeaders => "No Responders Requires Headers",
+        ClientClosedReason.AuthenticationExpired => "Authentication Expired",
         _ => reason.ToString(),
     };
 }

src/NATS.Server/NatsServer.cs

@@ -523,7 +523,7 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
         }
     }
 
-    private static void DeliverMessage(Subscription sub, string subject, string? replyTo,
+    private void DeliverMessage(Subscription sub, string subject, string? replyTo,
         ReadOnlyMemory<byte> headers, ReadOnlyMemory<byte> payload)
     {
         var client = sub.Client;
@@ -532,6 +532,16 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
         // Check auto-unsub
         var count = Interlocked.Increment(ref sub.MessageCount);
         if (sub.MaxMessages > 0 && count > sub.MaxMessages)
+        {
+            // Clean up exhausted subscription from trie and client tracking
+            var subList = client.Account?.SubList ?? _globalAccount.SubList;
+            subList.Remove(sub);
+            client.RemoveSubscription(sub.Sid);
+            return;
+        }
+
+        // Deny-list delivery filter
+        if (client.Permissions?.IsDeliveryAllowed(subject) == false)
             return;
 
         client.SendMessage(subject, sub.Sid, replyTo, headers, payload);

src/NATS.Server/Protocol/NatsProtocol.cs

@@ -33,6 +33,7 @@ public static class NatsProtocol
     public const string ErrPermissionsSubscribe = "Permissions Violation for Subscription";
     public const string ErrSlowConsumer = "Slow Consumer";
     public const string ErrNoRespondersRequiresHeaders = "No Responders Requires Headers Support";
+    public const string ErrMaxSubscriptionsExceeded = "Maximum Subscriptions Exceeded";
 }
 
 public sealed class ServerInfo

tests/NATS.Server.Tests/ClientClosedReasonTests.cs

@@ -5,10 +5,10 @@ public class ClientClosedReasonTests
     [Fact]
     public void All_expected_close_reasons_exist()
     {
-        // Verify all 17 enum values exist and are distinct (None + 16 named reasons)
+        // Verify all 18 enum values exist and are distinct (None + 17 named reasons)
         var values = Enum.GetValues<ClientClosedReason>();
-        values.Length.ShouldBe(17);
-        values.Distinct().Count().ShouldBe(17);
+        values.Length.ShouldBe(18);
+        values.Distinct().Count().ShouldBe(18);
     }
 
     [Theory]