fix(battle-node): assign turnState per side instead of hardcoding 0

Both PvP clients received turnState:0 ('both go first'). BuildBattleStart
now takes turnState; the Loaded arm assigns 0 to A, 1 to B — no Type check,
correct in Scripted (real player = A = first) and PvP (first arriver first).

Updated three existing BuildBattleStart callers in the test suite to pass
turnState:0 (the param is now required).

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

SVSim.BattleNode/Lifecycle/ScriptedLifecycle.cs

@@ -53,10 +53,10 @@ public static class ScriptedLifecycle
             bid: battleId);
 
     public static MsgEnvelope BuildBattleStart(
-        MatchContext selfCtx, MatchContext oppoCtx, long selfViewerId) =>
+        MatchContext selfCtx, MatchContext oppoCtx, long selfViewerId, int turnState) =>
         EnvelopeForPush(NetworkBattleUri.BattleStart,
             new BattleStartBody(
-                TurnState: 0,    // player goes first
+                TurnState: turnState,    // 0 = this side goes first, 1 = second. Caller decides.
                 BattleType: selfCtx.BattleType,
                 SelfInfo: new BattleStartSelfInfo(
                     Rank: ScriptedProfiles.PlayerRank,

SVSim.BattleNode/Sessions/BattleSession.cs

@@ -207,11 +207,19 @@ public sealed class BattleSession
                 break;
 
             case NetworkBattleUri.Loaded when phaseFrom?.Phase == BattleSessionPhase.AwaitingLoaded:
+            {
+                // Exactly one side goes first. A goes first deterministically: in Scripted that's
+                // the real player (constructed as A); in PvP that's the first arriver. No Type
+                // check — the rule is correct in both modes, and Bot/AINetwork never reaches this
+                // arm (its silent Loaded arm above wins the match). A per-battle coin-flip is a
+                // follow-up (see plan § Out of scope).
+                var turnState = ReferenceEquals(from, A) ? 0 : 1;
                 result.Add((from, ScriptedLifecycle.BuildBattleStart(
-                    from.Context, other.Context, from.ViewerId), false));
+                    from.Context, other.Context, from.ViewerId, turnState), false));
                 result.Add((from, ScriptedLifecycle.BuildDeal(), false));
                 phaseFrom!.Phase = BattleSessionPhase.AwaitingSwap;
                 break;
+            }
 
             case NetworkBattleUri.Swap when phaseFrom?.Phase == BattleSessionPhase.AwaitingSwap:
             {

SVSim.UnitTests/BattleNode/Lifecycle/ScriptedLifecycleTests.cs

@@ -71,7 +71,7 @@ public class ScriptedLifecycleTests
     [Test]
     public void BuildBattleStart_HasTurnStateZero_AndUsesContextBattleType()
     {
-        var env = ScriptedLifecycle.BuildBattleStart(FixtureCtx(), ScriptedBotCtx(), selfViewerId: 1);
+        var env = ScriptedLifecycle.BuildBattleStart(FixtureCtx(), ScriptedBotCtx(), selfViewerId: 1, turnState: 0);
         var body = (BattleStartBody)env.Body;
         Assert.That(body.TurnState, Is.EqualTo(0));
         Assert.That(body.BattleType, Is.EqualTo(11));
@@ -87,7 +87,7 @@ public class ScriptedLifecycleTests
             BattleType = 42,
         };
 
-        var env = ScriptedLifecycle.BuildBattleStart(ctx, ScriptedBotCtx(), selfViewerId: 1);
+        var env = ScriptedLifecycle.BuildBattleStart(ctx, ScriptedBotCtx(), selfViewerId: 1, turnState: 0);
         var body = (BattleStartBody)env.Body;
 
         Assert.That(body.SelfInfo.ClassId, Is.EqualTo("7"));

SVSim.UnitTests/BattleNode/Lifecycle/TypedBodyWireShapeTests.cs

@@ -86,7 +86,7 @@ public class TypedBodyWireShapeTests
     [Test]
     public void BuildBattleStart_SerializesAllWireKeysAndPreservesBattlePointAsymmetry()
     {
-        var env = ScriptedLifecycle.BuildBattleStart(FixtureCtx(), ScriptedBotCtx(), selfViewerId: 906243102);
+        var env = ScriptedLifecycle.BuildBattleStart(FixtureCtx(), ScriptedBotCtx(), selfViewerId: 906243102, turnState: 0);
 
         var json = MsgEnvelope.ToJson(env);
         var node = JsonNode.Parse(json)!.AsObject();

SVSim.UnitTests/BattleNode/Sessions/BattleSessionDispatchTests.cs

@@ -52,6 +52,43 @@ public class BattleSessionDispatchTests
         Assert.That(a.Phase, Is.EqualTo(BattleSessionPhase.AwaitingSwap));
     }
 
+    [Test]
+    public void Pvp_Loaded_from_A_assigns_turnState_0()
+    {
+        var (s, a, _) = NewPvpSession();
+        s.ComputeFrames(a, NewEnvelope(NetworkBattleUri.InitNetwork));
+        s.ComputeFrames(a, NewEnvelope(NetworkBattleUri.InitBattle));
+        var routes = s.ComputeFrames(a, NewEnvelope(NetworkBattleUri.Loaded));
+
+        var bs = (BattleStartBody)routes[0].Frame.Body;
+        Assert.That(bs.TurnState, Is.EqualTo(0), "A (first arriver) goes first.");
+    }
+
+    [Test]
+    public void Pvp_Loaded_from_B_assigns_turnState_1()
+    {
+        var (s, _, b) = NewPvpSession();
+        s.ComputeFrames(b, NewEnvelope(NetworkBattleUri.InitNetwork));
+        s.ComputeFrames(b, NewEnvelope(NetworkBattleUri.InitBattle));
+        var routes = s.ComputeFrames(b, NewEnvelope(NetworkBattleUri.Loaded));
+
+        var bs = (BattleStartBody)routes[0].Frame.Body;
+        Assert.That(bs.TurnState, Is.EqualTo(1), "B (second arriver) goes second.");
+    }
+
+    [Test]
+    public void Scripted_Loaded_from_player_assigns_turnState_0()
+    {
+        // Real player is constructed as A in scripted sessions, so it always goes first.
+        var (s, a, _) = NewSession();
+        s.ComputeFrames(a, NewEnvelope(NetworkBattleUri.InitNetwork));
+        s.ComputeFrames(a, NewEnvelope(NetworkBattleUri.InitBattle));
+        var routes = s.ComputeFrames(a, NewEnvelope(NetworkBattleUri.Loaded));
+
+        var bs = (BattleStartBody)routes[0].Frame.Body;
+        Assert.That(bs.TurnState, Is.EqualTo(0));
+    }
+
     [Test]
     public void Swap_pushes_SwapResponse_then_Ready_to_sender()
     {