fix(battle-node): emit envelope keys before body keys in MsgEnvelope.ToJson

Client RealTimeNetworkAgent.SetNetworkInfo iterates the synchronize-data
dict in insertion order. The "uri" key, when recognized as Matched, calls
GameMgr.InitializeSelfInfo which sets _selfDeck = null. Any "selfDeck"
processed before "uri" gets wiped; Matching.StartBattleLoad then crashes
on null.Select(...). Pre-refactor ToJson built a Dictionary envelope-first
then appended body keys, so the bug never surfaced. The typed-body rewrite
inverted the order — restoring envelope-first matches the prod wire.

Regression test BuildMatched_KeyOrder_PutsUriBeforeSelfDeckAndSelfInfo
locks the contract.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.BattleNode/Protocol/MsgEnvelope.cs

@@ -42,12 +42,24 @@ public sealed record MsgEnvelope(
 
     public static string ToJson(MsgEnvelope env)
     {
-        JsonObject result;
+        // Envelope fields MUST come before body fields on the wire. The client's
+        // RealTimeNetworkAgent.SetNetworkInfo iterates the dict in insertion order and
+        // clears _selfDeck on the "uri" key (via GameMgr.InitializeSelfInfo). Any body
+        // field processed before "uri" is wiped before Matching.StartBattleLoad reads
+        // it back. The prod wire emits envelope keys first; we must too.
+        var result = new JsonObject();
+        result["uri"] = env.Uri.ToString();
+        result["viewerId"] = env.ViewerId;
+        result["uuid"] = env.Uuid;
+        result["try"] = env.Try;
+        result["cat"] = (int)env.Cat;
+        if (env.Bid is not null) result["bid"] = env.Bid;
+        if (env.PubSeq.HasValue) result["pubSeq"] = env.PubSeq.Value;
+        if (env.PlaySeq.HasValue) result["playSeq"] = env.PlaySeq.Value;
+
         if (env.Body is RawBody raw)
         {
-            // Inbound-echo path: flatten Entries to top-level keys, same as before
-            // the typed-body refactor.
-            result = new JsonObject();
+            // Inbound-echo path: flatten Entries to top-level keys.
             foreach (var (k, v) in raw.Entries)
             {
                 if (ReservedEnvelopeKeys.Contains(k))
@@ -60,19 +72,17 @@ public sealed record MsgEnvelope(
         }
         else
         {
-            // Typed body: serialize via [JsonPropertyName] attributes on the record.
-            result = (JsonObject)JsonSerializer.SerializeToNode(env.Body, env.Body.GetType(), Options)!;
+            // Typed body: serialize via [JsonPropertyName] attributes on the record,
+            // then layer each field onto `result` after the envelope keys. DeepClone
+            // because S.T.Json JsonNodes can only have one parent; reassigning a node
+            // owned by `bodyNode` to `result` would throw without the clone.
+            var bodyNode = (JsonObject)JsonSerializer.SerializeToNode(env.Body, env.Body.GetType(), Options)!;
+            foreach (var prop in bodyNode)
+            {
+                result[prop.Key] = prop.Value?.DeepClone();
+            }
         }
 
-        result["uri"] = env.Uri.ToString();
-        result["viewerId"] = env.ViewerId;
-        result["uuid"] = env.Uuid;
-        result["try"] = env.Try;
-        result["cat"] = (int)env.Cat;
-        if (env.Bid is not null) result["bid"] = env.Bid;
-        if (env.PubSeq.HasValue) result["pubSeq"] = env.PubSeq.Value;
-        if (env.PlaySeq.HasValue) result["playSeq"] = env.PlaySeq.Value;
-
         return result.ToJsonString(Options);
     }
 

SVSim.UnitTests/BattleNode/Lifecycle/TypedBodyWireShapeTests.cs

@@ -16,6 +16,31 @@ namespace SVSim.UnitTests.BattleNode.Lifecycle;
 [TestFixture]
 public class TypedBodyWireShapeTests
 {
+    [Test]
+    public void BuildMatched_KeyOrder_PutsUriBeforeSelfDeckAndSelfInfo()
+    {
+        // Regression: the client's RealTimeNetworkAgent.SetNetworkInfo iterates the
+        // synchronize-data dict in insertion order. When it hits "uri" and recognizes
+        // "Matched", it calls GameMgr.InitializeSelfInfo() which sets _selfDeck = null.
+        // Any "selfDeck" / "selfInfo" key processed BEFORE "uri" is wiped before
+        // Matching.StartBattleLoad reads it back, and GetSelfDeck().Select(...) crashes
+        // with "Value cannot be null. Parameter name: source". The prod wire format
+        // emits envelope keys (uri first) before body keys; we must too.
+        var env = ScriptedLifecycle.BuildMatched(
+            playerViewerId: 1, opponentViewerId: 2, battleId: "b");
+        var json = MsgEnvelope.ToJson(env);
+
+        var uriIdx = json.IndexOf("\"uri\":", StringComparison.Ordinal);
+        var selfDeckIdx = json.IndexOf("\"selfDeck\":", StringComparison.Ordinal);
+        var selfInfoIdx = json.IndexOf("\"selfInfo\":", StringComparison.Ordinal);
+
+        Assert.That(uriIdx, Is.GreaterThan(-1), "uri must be present");
+        Assert.That(selfDeckIdx, Is.GreaterThan(-1), "selfDeck must be present");
+        Assert.That(selfInfoIdx, Is.GreaterThan(-1), "selfInfo must be present");
+        Assert.That(uriIdx, Is.LessThan(selfDeckIdx), "uri must appear BEFORE selfDeck");
+        Assert.That(uriIdx, Is.LessThan(selfInfoIdx), "uri must appear BEFORE selfInfo");
+    }
+
     [Test]
     public void BuildMatched_SerializesAllWireKeysExpectedByTheClient()
     {