feat: implement full MQTT Go parity across 5 phases — binary protocol, auth/TLS, cross-protocol bridging, monitoring, and JetStream persistence

Phase 1: Binary MQTT 3.1.1 wire protocol with PipeReader-based parsing,
full packet type dispatch, and MQTT 3.1.1 compliance checks.

Phase 2: Auth pipeline routing MQTT CONNECT through AuthService,
TLS transport with SslStream wrapping, pinned cert validation.

Phase 3: IMessageRouter refactor (NatsClient → INatsClient),
MqttNatsClientAdapter for cross-protocol bridging, MqttTopicMapper
with full Go-parity topic/subject translation.

Phase 4: /connz mqtt_client field population, /varz actual MQTT port.

Phase 5: JetStream persistence — MqttStreamInitializer creates 5
internal streams, MqttConsumerManager for QoS 1/2 consumers,
subject-keyed session/retained lookups replacing linear scans.

All 503 MQTT tests and 1589 Core tests pass.

src/NATS.Server/Mqtt/MqttQoS1Tracker.cs

@@ -1,6 +1,7 @@
-// QoS 1 outgoing message tracker for MQTT.
+// QoS 1 outgoing message tracker for MQTT with JetStream ack integration.
 // Go reference: golang/nats-server/server/mqtt.go
 //   QoS 1 outbound tracking — mqttProcessPub (~line 1200)
+//   trackPublish — maps packet IDs to stream sequences for ack tracking.
 
 using System.Collections.Concurrent;
 
@@ -8,8 +9,8 @@ namespace NATS.Server.Mqtt;
 
 /// <summary>
 /// Tracks outgoing QoS 1 messages pending PUBACK from the client.
-/// Messages are stored with their packet ID and can be redelivered on reconnect.
-/// Go reference: server/mqtt.go — mqttProcessPub (QoS 1 outbound tracking).
+/// Maps packet IDs to JetStream stream sequences for ack-based cleanup.
+/// Go reference: server/mqtt.go — mqttProcessPub, trackPublish.
 /// </summary>
 public sealed class MqttQoS1Tracker
 {
@@ -24,7 +25,7 @@ public sealed class MqttQoS1Tracker
     /// Registers an outgoing QoS 1 message and assigns a packet ID.
     /// Returns the assigned packet ID.
     /// </summary>
-    public ushort Register(string topic, byte[] payload)
+    public ushort Register(string topic, byte[] payload, ulong streamSequence = 0)
     {
         var id = GetNextPacketId();
         _pending[id] = new QoS1PendingMessage
@@ -34,17 +35,18 @@ public sealed class MqttQoS1Tracker
             Payload = payload,
             SentAtUtc = DateTime.UtcNow,
             DeliveryCount = 1,
+            StreamSequence = streamSequence,
         };
         return id;
     }
 
     /// <summary>
     /// Acknowledges receipt of a PUBACK for the given packet ID.
-    /// Returns true if the message was found and removed.
+    /// Returns the pending message if found, or null.
     /// </summary>
-    public bool Acknowledge(ushort packetId)
+    public QoS1PendingMessage? Acknowledge(ushort packetId)
     {
-        return _pending.TryRemove(packetId, out _);
+        return _pending.TryRemove(packetId, out var msg) ? msg : null;
     }
 
     /// <summary>
@@ -93,4 +95,11 @@ public sealed class QoS1PendingMessage
     public byte[] Payload { get; init; } = [];
     public DateTime SentAtUtc { get; set; }
     public int DeliveryCount { get; set; } = 1;
+
+    /// <summary>
+    /// JetStream stream sequence for this message. 0 if not backed by JetStream.
+    /// Used to ack the message in the stream on PUBACK.
+    /// Go reference: server/mqtt.go trackPublish — maps packet ID → stream sequence.
+    /// </summary>
+    public ulong StreamSequence { get; init; }
 }