Card choice from hand as an effect cost

AskHandCardChoice pauses on the hand and returns the chosen card, so abilities can pay discard costs interactively. Knight of Rose, Morgana implemented: on attack, optionally discard a card for +4000 until end of turn. Test covers the full pause chain and the return to the guard step.

IMPLEMENTATION_CHECKLIST.md

@@ -120,6 +120,7 @@
 - [x] Выбор целей: `PendingChoice` + `ChooseCommand`, используется Blaster Blade для уничтожения Арьергарда противника.
 - [ ] Стоимости: CB, SB, discard, rest self, retire self, put to soul, return to deck.
 - [x] Выбор цели игроком (`PendingChoice` / `ChooseCommand`); «до N» / «ровно N» ещё нет.
+- [x] Выбор карты из руки как стоимости эффекта (Morgana: сброс → +4000).
 - [x] Поиск в колоде без просмотра: 0 совпадений — уведомление и перемешивание, 1 — сразу в руку, несколько — выбор; разные арты считаются разными картами.
 - [x] Поиск с призывом в круг Арьергарда (Alfred) и с райдом (API, Llew).
 - [x] Просмотр верхней карты с решением «оставить на верху / положить в низ» (Cocoa).

server/src/Vanguard.Rules/Engine/Abilities/CardScripts.cs

@@ -20,9 +20,42 @@ public static class CardScripts
             ["tyrant-deathrex"] = new DeathrexScript(),
             ["demon-eater"] = new DemonEaterScript(),
             ["maiden-of-libra"] = new MaidenOfLibraScript(),
+            ["knight-of-rose-morgana"] = new MorganaScript(),
         };
 }
 
+/// <summary>
+/// Knight of Rose, Morgana: при атаке можно сбросить карту из руки и получить +4000 до конца хода.
+/// </summary>
+public sealed class MorganaScript : CardScript
+{
+    public override string NameId => "knight-of-rose-morgana";
+
+    public override IEnumerable<AbilityDefinition> Abilities
+    {
+        get
+        {
+            yield return new AbilityDefinition
+            {
+                Trigger = AbilityTrigger.OnAttackDeclared,
+                Optional = true,
+                CanPay = ctx => ctx.State.Players[ctx.Owner].Hand.Count > 0,
+                Resolve = ctx => ctx.Engine.AskHandCardChoice(
+                    ctx.Owner,
+                    "Сбросьте карту из руки",
+                    null,
+                    card =>
+                    {
+                        var p = ctx.State.Players[ctx.Owner];
+                        p.Hand.Remove(card);
+                        p.Drop.Add(card);
+                        ctx.Source.TemporaryPower += 4000;
+                    }),
+            };
+        }
+    }
+}
+
 /// <summary>Tyrant, Deathrex: когда эта карта атакует, получает +5000 до конца боя.</summary>
 public sealed class DeathrexScript : CardScript
 {

server/src/Vanguard.Rules/Engine/GameEngine.cs

@@ -692,6 +692,33 @@ public sealed class GameEngine
     public bool HasEmptyRearGuard(int player) =>
         State.Players[player].RearGuards.Any(u => u is null);
 
+    /// <summary>Выбор карты из руки (стоимость, сброс, цель эффекта).</summary>
+    public void AskHandCardChoice(
+        int player,
+        string prompt,
+        Func<CardInstance, bool>? predicate,
+        Action<CardInstance> onChosen)
+    {
+        var cards = State.Players[player].Hand
+            .Where(c => predicate is null || predicate(c))
+            .ToList();
+
+        if (cards.Count == 0)
+            return;
+
+        State.PendingChoice = new PendingChoice
+        {
+            Player = player,
+            Prompt = prompt,
+            Options = cards
+                .Select((card, index) => new ChoiceOption(index, State.Catalog.CardOf(card.PrintingId).NameEn))
+                .ToList(),
+            Resolve = index => onChosen(cards[index]),
+        };
+        State.Step = Step.Choice;
+        State.ActivePlayer = player;
+    }
+
     public void AskEmptyRearGuardChoice(int player, string prompt, Action<int> onChosen)
     {
         var slots = Enumerable.Range(0, PlayerState.RearGuardSlots)

server/tests/Vanguard.Rules.Tests/GameEngineTests.cs

@@ -26,6 +26,7 @@ public class GameEngineTests
     private const string Libra = "BT01/017EN";     // OTT, grade 2
     private const string Deathrex = "BT01/033EN";   // Tachikaze, 10000
     private const string DemonEater = "BT01/036EN"; // Dark Irregulars, 10000
+    private const string Morgana = "TD01/011EN";    // Royal Paladin, grade 1, discard +4000
 
     [Fact]
     public void Start_Places_Starting_Vanguard_And_Draws_Five()
@@ -940,6 +941,30 @@ public class GameEngineTests
         Assert.NotNull(engine.State.PendingAbility);
     }
 
+    [Fact]
+    public void Morgana_Discards_To_Gain_4000_When_Attacking()
+    {
+        var engine = StartedEngine();
+        engine.Execute(new SkipRideCommand());
+        SetVanguard(engine, 0, Morgana);
+        engine.Execute(new EnterBattleCommand());
+
+        var morgana = engine.State.Players[0].Vanguard!;
+        var handBefore = engine.State.Players[0].Hand.Count;
+
+        Assert.True(engine.Execute(new AttackCommand(-1, -1)).Accepted);
+        Assert.NotNull(engine.State.PendingAbility);
+
+        Assert.True(engine.Execute(new ResolveAbilityCommand(true)).Accepted);
+        Assert.NotNull(engine.State.PendingChoice);
+
+        Assert.True(engine.Execute(new ChooseCommand(0)).Accepted);
+
+        Assert.Equal(4000, morgana.TemporaryPower);
+        Assert.Equal(handBefore - 1, engine.State.Players[0].Hand.Count);
+        Assert.Equal(Step.Guard, engine.State.Step);
+    }
+
     [Fact]
     public void ResolveTrigger_Rejects_When_Nothing_Is_Pending()
     {
@@ -1079,6 +1104,7 @@ public class GameEngineTests
         (Lien, 2),
         (Cocoa, 2), (Libra, 2),
         (Deathrex, 2), (DemonEater, 2),
+        (Morgana, 2),
     };
 
     private List<string> BuildDeck()