fix(battle-node): involuntary-drop survivor gets DisconnectWin, not Win=NoContest

Code-review follow-up to the dispatch unification (0a8a84b).

1. The RunAsync drop cascade synthesized BattleFinish(Win=1), which the client
   renders as RESULT_CODE.NoContest ("battle ended in no contest") instead of a
   win. Add DisconnectWin=201 (already in the client enum, routes to WIN UI) and
   ship it for involuntary opponent drops. Update PvpMidGameDisconnect_FullCascade.

2. Remove BuildBattleFinishNoContest() — dead since the Retire/Kill arm moved to
   RetireWin/RetireLose.

3. Correct the BattleResult docstring: Lose/Win/Consistency are no longer emitted
   by any dispatch arm; they survive only as serialization-test constants.

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

SVSim.BattleNode/Protocol/BattleResult.cs

@@ -30,12 +30,15 @@ namespace SVSim.BattleNode.Protocol;
 /// reproduction that exposed the inversion.
 /// </para>
 /// <para>
-/// The pre-2026-06-02 <c>Lose = 0</c> / <c>Win = 1</c> / <c>Consistency = 2</c>
-/// values are kept for the existing Retire/Kill Scripted flow (which ships
-/// <c>Win = 1</c>, parsed client-side as <c>RESULT_CODE.NoContest</c> and
-/// rendered as "battle ended in no contest" — works in that the battle
-/// terminates, but shows the wrong text). To be removed once that flow is
-/// rewritten to use the proper retire codes.
+/// The legacy <c>Lose = 0</c> / <c>Win = 1</c> / <c>Consistency = 2</c> values
+/// (client <c>RESULT_CODE.NotFinish</c> / <c>NoContest</c> / <c>Invalid</c>) are
+/// no longer emitted by any dispatch arm: the Retire/Kill flow now ships the
+/// proper <c>RetireWin</c> / <c>RetireLose</c> codes, and the involuntary-drop
+/// cascade ships <c>DisconnectWin</c>. They survive only as wire-constant
+/// references in serialization tests and can be deleted once those are dropped.
+/// (Historically <c>Win = 1</c> was shipped on Retire and rendered client-side
+/// as "battle ended in no contest" — the wrong text — which is why it was
+/// replaced.)
 /// </para>
 /// <para>
 /// Always serialize as the int value, not the name; see the
@@ -71,4 +74,11 @@ public enum BattleResult
 
     /// <summary>Player lost by retiring. Pushed to the retirer on <c>Retire</c>/<c>Kill</c>.</summary>
     RetireLose = 106,
+
+    /// <summary>Survivor wins because the opponent's socket dropped without a graceful
+    /// <c>Retire</c>. Pushed to the survivor by the <see cref="Sessions.BattleSession"/>
+    /// RunAsync drop cascade. Client <c>RESULT_CODE.DisconnectWin</c> renders the
+    /// "opponent disconnected" result text → player WIN UI. Same player-perspective
+    /// convention as the Life/Retire codes.</summary>
+    DisconnectWin = 201,
 }

SVSim.BattleNode/Sessions/BattleSession.cs

@@ -58,11 +58,13 @@ public sealed class BattleSession
 
             if (Phase != BattleSessionPhase.Terminal)
             {
-                // Involuntary drop (no graceful Retire): synthesize BattleFinish(Win) to survivor.
+                // Involuntary drop (no graceful Retire): synthesize BattleFinish(DisconnectWin)
+                // to survivor. DisconnectWin=201 → client renders "opponent disconnected" →
+                // WIN UI; the legacy Win=1 used here previously rendered "no contest".
                 try
                 {
                     await survivor.PushAsync(
-                        BuildBattleFinish(BattleResult.Win), noStock: true, cancellation)
+                        BuildBattleFinish(BattleResult.DisconnectWin), noStock: true, cancellation)
                         .ConfigureAwait(false);
                 }
                 catch (Exception ex)
@@ -334,17 +336,6 @@ public sealed class BattleSession
         PlaySeq: null,
         Body: new ResultCodeOnlyBody());
 
-    private MsgEnvelope BuildBattleFinishNoContest() => new(
-        NetworkBattleUri.BattleFinish,
-        ViewerId: ScriptedLifecycle.FakeOpponentViewerId,
-        Uuid: WireConstants.ServerUuid,
-        Bid: null,
-        Try: 0,
-        Cat: EmitCategory.Battle,
-        PubSeq: null,
-        PlaySeq: null,
-        Body: new BattleFinishBody(Result: BattleResult.Win));
-
     private MsgEnvelope BuildTurnEndBroadcast() => new(
         NetworkBattleUri.TurnEnd,
         ViewerId: ScriptedLifecycle.FakeOpponentViewerId,

SVSim.UnitTests/BattleNode/Integration/BattleNodeFlowTests.cs

@@ -320,11 +320,11 @@ public class BattleNodeFlowTests
         // Abruptly close A's WS (no Retire).
         await clientA.DisposeAsync();
 
-        // B should receive BattleFinish(Win) within a few seconds.
+        // B should receive BattleFinish(DisconnectWin) within a few seconds.
         var bFinish = await clientB.ReceiveSynchronizeAsync(ct);
         Assert.That(bFinish.Uri, Is.EqualTo(NetworkBattleUri.BattleFinish));
         var bBody = (RawBody)bFinish.Body;
-        Assert.That((long)bBody.Entries["result"]!, Is.EqualTo((long)SVSim.BattleNode.Protocol.BattleResult.Win));
+        Assert.That((long)bBody.Entries["result"]!, Is.EqualTo((long)SVSim.BattleNode.Protocol.BattleResult.DisconnectWin));
 
         // PendingBattle should be evicted by the second arriver's RemovePending.
         var store = factory.Services.GetRequiredService<SVSim.BattleNode.Sessions.IBattleSessionStore>();