feat(battle-node): CountHiddenDraws — hidden shared-RNG draw tally for real spin

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

SVSim.UnitTests/BattleNode/Sessions/KnownListBuilderTests.cs

@@ -20,6 +20,78 @@ public class KnownListBuilderTests
         }
     };
 
+    // A move op dict allowing extra keys (e.g. "rand") for CountHiddenDraws fixtures.
+    private static Dictionary<string, object?> MoveOp(long[] idxs, int from, int to,
+        IDictionary<string, object?>? extra = null)
+    {
+        var move = new Dictionary<string, object?>
+        {
+            ["idx"] = idxs.Select(i => (object?)i).ToList(),
+            ["isSelf"] = 1L, ["from"] = (long)from, ["to"] = (long)to,
+        };
+        if (extra is not null) foreach (var kv in extra) move[kv.Key] = kv.Value;
+        return new Dictionary<string, object?> { ["move"] = move };
+    }
+
+    private static readonly IReadOnlySet<int> NoneRevealed = new HashSet<int>();
+
+    [Test]
+    public void CountHiddenDraws_counts_a_hidden_deck_to_hand_fetch()
+    {
+        // Hoverboard-shaped: move(0->10) for a non-played, unrevealed token idx.
+        var orderList = new List<object?> { MoveOp(new[] { 31L }, from: 0, to: 10) };
+        Assert.That(KnownListBuilder.CountHiddenDraws(orderList, playIdx: 3, NoneRevealed), Is.EqualTo(1));
+    }
+
+    [Test]
+    public void CountHiddenDraws_ignores_the_played_cards_own_move()
+    {
+        // The played card moving hand(10)->field(20) is not a draw.
+        var orderList = new List<object?> { MoveOp(new[] { 3L }, from: 10, to: 20) };
+        Assert.That(KnownListBuilder.CountHiddenDraws(orderList, playIdx: 3, NoneRevealed), Is.EqualTo(0));
+    }
+
+    [Test]
+    public void CountHiddenDraws_ignores_a_visible_destroy()
+    {
+        // A visible field(20)->cemetery(30) destroy is reproduced by the receiver → 0.
+        var orderList = new List<object?> { MoveOp(new[] { 8L }, from: 20, to: 30) };
+        Assert.That(KnownListBuilder.CountHiddenDraws(orderList, playIdx: 3, NoneRevealed), Is.EqualTo(0));
+    }
+
+    [Test]
+    public void CountHiddenDraws_ignores_a_revealed_fetch()
+    {
+        // The fetched idx's identity was revealed to the opponent (in `revealed`) → 0.
+        var orderList = new List<object?> { MoveOp(new[] { 31L }, from: 0, to: 10) };
+        var revealed = new HashSet<int> { 31 };
+        Assert.That(KnownListBuilder.CountHiddenDraws(orderList, playIdx: 3, revealed), Is.EqualTo(0));
+    }
+
+    [Test]
+    public void CountHiddenDraws_ignores_a_lot_based_random()
+    {
+        // A move op carrying a `rand` array is reproduced (re-rolled) by the receiver → 0.
+        var rand = new Dictionary<string, object?> { ["rand"] = new List<object?> { 0.5d } };
+        var orderList = new List<object?> { MoveOp(new[] { 31L }, from: 0, to: 10, extra: rand) };
+        Assert.That(KnownListBuilder.CountHiddenDraws(orderList, playIdx: 3, NoneRevealed), Is.EqualTo(0));
+    }
+
+    [Test]
+    public void CountHiddenDraws_counts_each_hidden_card_in_a_multi_fetch()
+    {
+        var orderList = new List<object?> { MoveOp(new[] { 31L, 32L }, from: 0, to: 10) };
+        Assert.That(KnownListBuilder.CountHiddenDraws(orderList, playIdx: 3, NoneRevealed), Is.EqualTo(2));
+    }
+
+    [Test]
+    public void CountHiddenDraws_returns_zero_for_a_vanilla_play()
+    {
+        var orderList = new List<object?> { MoveOp(new[] { 3L }, from: 10, to: 20) };
+        Assert.That(KnownListBuilder.CountHiddenDraws(orderList, playIdx: 3, NoneRevealed), Is.EqualTo(0));
+        Assert.That(KnownListBuilder.CountHiddenDraws(null, playIdx: 3, NoneRevealed), Is.EqualTo(0));
+    }
+
     [Test]
     public void ExtractMoveTo_returns_to_for_matching_idx()
     {