feat: add jetstream publish preconditions and dedupe

src/NATS.Server/JetStream/Publish/JetStreamPublisher.cs

@@ -3,6 +3,7 @@ namespace NATS.Server.JetStream.Publish;
 public sealed class JetStreamPublisher
 {
     private readonly StreamManager _streamManager;
+    private readonly PublishPreconditions _preconditions = new();
 
     public JetStreamPublisher(StreamManager streamManager)
     {
@@ -10,7 +11,20 @@ public sealed class JetStreamPublisher
     }
 
     public bool TryCapture(string subject, ReadOnlyMemory<byte> payload, out PubAck ack)
+        => TryCapture(subject, payload, null, out ack);
+
+    public bool TryCapture(string subject, ReadOnlyMemory<byte> payload, string? msgId, out PubAck ack)
     {
+        if (_preconditions.IsDuplicate(msgId, out var existingSequence))
+        {
+            ack = new PubAck
+            {
+                Seq = existingSequence,
+                ErrorCode = 10071,
+            };
+            return true;
+        }
+
         var captured = _streamManager.Capture(subject, payload);
         if (captured == null)
         {
@@ -19,7 +33,7 @@ public sealed class JetStreamPublisher
         }
 
         ack = captured;
-
+        _preconditions.Record(msgId, ack.Seq);
         return true;
     }
 }