feat(battle-node): emit real spin per-frame on forwarded PlayActions

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

SVSim.BattleNode/Sessions/Dispatch/Handlers/PlayActionsHandler.cs

@@ -48,6 +48,17 @@ internal sealed class PlayActionsHandler : IFrameHandler
         // knownList in the same frame (capture line 75).
         var uList = KnownListBuilder.RelayUList(entries.GetValueOrDefault("uList"));
 
+        // Hidden shared-RNG draws (a random deck→hand fetch the opponent can't reproduce) advance the
+        // sender's shared _stableRandom; the receiver doesn't re-run them, so it needs a spin crank to
+        // stay aligned for later visible randoms. Per-frame delivery (real-spin design §3.2): the count
+        // rides THIS PlayActions. A fetch we relay with an identity (uList cardId present) is already
+        // known to the opponent — exclude its idxs so it isn't counted. 0 → null (omitted; client
+        // assumes spin:0).
+        var revealed = uList is null
+            ? (IReadOnlySet<int>)new HashSet<int>()
+            : uList.Where(u => u.CardId is not null).SelectMany(u => u.IdxList).ToHashSet();
+        var spin = KnownListBuilder.CountHiddenDraws(orderList, playIdx, revealed);
+
         var body = new PlayActionsBroadcastBody(
             PlayIdx: playIdx,
             Type: type,
@@ -56,7 +67,8 @@ internal sealed class PlayActionsHandler : IFrameHandler
             UList: uList,
             // {type,cardId} forwarded so the opponent renders the choice token; selectCard dropped
             // when open==0 (hidden draw-to-hand pick). Null for a vanilla play (no keyAction).
-            KeyAction: KnownListBuilder.StripKeyActionForOpponent(keyAction));
+            KeyAction: KnownListBuilder.StripKeyActionForOpponent(keyAction),
+            Spin: spin > 0 ? spin : null);
 
         var frame = ctx.Env with { Body = body };
         return new[] { new DispatchRoute(ctx.Other, frame, false) };