refactor(battle-node): cut handler over to BattleSessionV2 + participants

Production WS path now constructs RealParticipant + ScriptedBotParticipant
and hands them to BattleSessionV2 instead of the old single-WS
BattleSession. Wire behaviour preserved end-to-end (BattleNodeFlowTests
still pass).

Also fixes a RunAsync bug uncovered by the cutover: WhenAny would
terminate the session as soon as the scripted bot's no-op RunAsync
resolved, killing the live WS read loop before any traffic arrived.
Phase 1 semantics are simpler — wait for ALL participants. Phase 2's
Pvp disconnect propagation will revisit this.

SVSim.BattleNode/Hosting/BattleNodeWebSocketHandler.cs

@@ -1,6 +1,7 @@
 using Microsoft.AspNetCore.Http;
 using Microsoft.Extensions.Logging;
 using SVSim.BattleNode.Sessions;
+using SVSim.BattleNode.Sessions.Participants;
 using SVSim.BattleNode.Wire;
 
 namespace SVSim.BattleNode.Hosting;
@@ -104,9 +105,21 @@ public sealed class BattleNodeWebSocketHandler
 
         var ws = await ctx.WebSockets.AcceptWebSocketAsync();
         _store.RemovePending(battleId);
-        // Phase 1: handler still constructs the old single-WS BattleSession.
+
-        // Task 9 switches to BattleSessionV2 + RealParticipant + ScriptedBotParticipant.
+        // Phase 1: only Scripted is wired; Pvp + Bot land in subsequent phases.
-        var session = new BattleSession(ws, battleId, viewerId, pending.P1.Context, _loggerFactory.CreateLogger<BattleSession>());
+        if (pending.Type != BattleType.Scripted)
+        {
+            _log.LogWarning(
+                "WS upgrade for BattleId={Bid} with unsupported type={Type} (Phase 1 only handles Scripted).",
+                battleId, pending.Type);
+            return;
+        }
+
+        var realParticipant = new RealParticipant(ws, viewerId, pending.P1.Context,
+            _loggerFactory.CreateLogger<RealParticipant>());
+        var scriptedBot = new ScriptedBotParticipant();
+        var session = new BattleSessionV2(battleId, pending.Type, realParticipant, scriptedBot,
+            _loggerFactory.CreateLogger<BattleSessionV2>());
         await session.RunAsync(ctx.RequestAborted);
     }
 

SVSim.BattleNode/Sessions/BattleSessionV2.cs

@@ -42,13 +42,13 @@ public sealed class BattleSessionV2
 
     public async Task RunAsync(CancellationToken cancellation)
     {
-        // Run both participants' inbound loops in parallel. First to complete cancels
+        // Run both participants' inbound loops in parallel and wait for them all to
-        // the session via the outer cancellation token.
+        // complete. NoOp/Scripted bots return immediately; Real returns when the WS
-        using var cts = CancellationTokenSource.CreateLinkedTokenSource(cancellation);
+        // closes. Using WhenAny here would have killed the session as soon as the
-        var aTask = A.RunAsync(cts.Token);
+        // scripted bot's no-op RunAsync resolved. Phase 2's Pvp/Bot cases will need
-        var bTask = B.RunAsync(cts.Token);
+        // disconnect propagation; that's wired in their own task.
-        await Task.WhenAny(aTask, bTask);
+        var aTask = A.RunAsync(cancellation);
-        cts.Cancel();
+        var bTask = B.RunAsync(cancellation);
         try { await Task.WhenAll(aTask, bTask); } catch { /* swallow cancellation */ }
 
         await Task.WhenAll(