Add optional Zero field to ScriptPacket for step ack (#438)

* Add ScriptCompletePacket for official "script 0 <id> <step>" ack

The official NosTale server emits `script 0 <scriptId> <stepId>` after
each tutorial script step to acknowledge completion. Without it the
client freezes on interactive steps (e.g. the quest accept dialog does
nothing when pressed). The existing ScriptPacket only covers the
2-field `script <scriptId> <stepId>` form used to enter a step, so this
adds a sibling ServerPackets class with a literal leading `0` to match
the ack shape.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Add optional leading Zero field to ScriptPacket for step ack

The official NosTale server emits two `script` shapes: `script <scriptId>
<stepId>` to enter a step, and `script 0 <scriptId> <stepId>` to
acknowledge that step has completed. Without the ack the client freezes
on interactive steps (e.g. the quest-accept dialog does nothing when
pressed). Add an optional leading Zero byte so the same packet class
emits both shapes — Zero=null for advance, Zero=0 for ack.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: erwan-joly

src/NosCore.Packets/NosCore.Packets.csproj

@@ -12,7 +12,7 @@
 		<RepositoryUrl>https://github.com/NosCoreIO/NosCore.Packets.git</RepositoryUrl>
 		<PackageIconUrl></PackageIconUrl>
 		<PackageTags>nostale, noscore, chickenapi, nostale private server source, nostale emulator</PackageTags>
-		<Version>16.7.0</Version>
+		<Version>16.8.0</Version>
 		<PackageRequireLicenseAcceptance>false</PackageRequireLicenseAcceptance>
 		<Description>NosCore's Packets (Nostale packets) defined over classes</Description>
 		<PackageLicenseExpression>MIT</PackageLicenseExpression>

src/NosCore.Packets/ServerPackets/Quest/ScriptPacket.cs

@@ -12,10 +12,13 @@ namespace NosCore.Packets.ServerPackets.Quest
     [PacketHeader("script", Scope.InGame)]
     public class ScriptPacket : PacketBase
     {
-        [PacketIndex(0)]
-        public int ScriptId { get; set; }
+        [PacketIndex(0, IsOptional = true)]
+        public byte? Zero { get; set; }
 
         [PacketIndex(1)]
+        public int ScriptId { get; set; }
+
+        [PacketIndex(2)]
         public int ScriptStepId { get; set; }
     }
 }

test/NosCore.Packets.Tests/SerializerTest.cs

@@ -59,6 +59,7 @@ public class SerializationTests
                 typeof(MlobjlstPacket),
                 typeof(SuccessPacket),
                 typeof(TargetOffPacket),
+                typeof(ScriptPacket),
                 typeof(GuriPacket),
                 typeof(BiPacket),
                 typeof(MsgiPacket),
@@ -167,6 +168,33 @@ public void SerializeInheritedPacket()
             Assert.AreEqual("targetoff 57 149 1 1997", packet);
         }
 
+        [TestMethod]
+        public void SerializeScriptPacketAdvance()
+        {
+            var testPacket = new ScriptPacket
+            {
+                ScriptId = 1,
+                ScriptStepId = 80
+            };
+
+            var packet = Serializer.Serialize(testPacket);
+            Assert.AreEqual("script 1 80", packet);
+        }
+
+        [TestMethod]
+        public void SerializeScriptPacketComplete()
+        {
+            var testPacket = new ScriptPacket
+            {
+                Zero = 0,
+                ScriptId = 1,
+                ScriptStepId = 80
+            };
+
+            var packet = Serializer.Serialize(testPacket);
+            Assert.AreEqual("script 0 1 80", packet);
+        }
+
         [TestMethod]
         public void SerializeRecursiveListSubPackets()
         {