fix(game-server): adopt client packet sequences on first packet

The Cycle client does not derive its initial packet sequences from the
handshake cookie the way stock UE does (its acked server-seq isn't present
anywhere in the cookie), so the cookie-based InitSequence disagreed and
every post-handshake packet was rejected as out-of-order. On the first
packet, adopt the client's announced Seq/AckedSeq instead.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/Prospect.Unreal/Net/UNetConnection.cs

@@ -267,6 +267,8 @@ public abstract class UNetConnection : UPlayer
     /// <summary>
     ///     Full incoming packet index.
     /// </summary>
+    private bool _bAdoptedInitialSequence;
+
     public int InPacketId { get; private set; }
     
     /// <summary>
@@ -540,6 +542,25 @@ public abstract class UNetConnection : UPlayer
             }
 
             var packetSequenceDelta = PacketNotify.GetSequenceDelta(header);
+
+            // The Cycle client doesn't derive its initial packet sequences from the handshake
+            // cookie the way stock UE does, so our cookie-based InitSequence disagrees with it
+            // and every packet looks out-of-order. On the very first packet, adopt the client's
+            // announced sequences (Seq + AckedSeq) instead of the cookie-derived ones.
+            if (packetSequenceDelta <= 0 && !_bAdoptedInitialSequence && Driver != null && Driver.IsServer())
+            {
+                _bAdoptedInitialSequence = true;
+                var adoptIn = new SequenceNumber((ushort)(header.Seq.Value - 1));
+                var adoptOut = new SequenceNumber((ushort)(header.AckedSeq.Value + 1));
+                PacketNotify.Init(adoptIn, adoptOut);
+                InPacketId = header.Seq.Value - 1;
+                OutPacketId = header.AckedSeq.Value + 1;
+                OutAckPacketId = header.AckedSeq.Value;
+                LastNotifiedPacketId = OutAckPacketId;
+                Logger.Information("[HS-SEQ] Adopted client sequences: inSeq={In} outSeq={Out}", header.Seq.Value, header.AckedSeq.Value + 1);
+                packetSequenceDelta = PacketNotify.GetSequenceDelta(header);
+            }
+
             if (packetSequenceDelta > 0)
             {
                 var bPacketOrderCacheActive = !_bFlushingPacketOrderCache && _packetOrderCache != null;