fix: StepTurn回合流转重构 + 碰/杠牌数修正

Root cause:
1. 摸牌在碰/杠检测之前→摸的牌浪费→手牌净减
2. RemoveAll一次删光所有同牌→碰2张变删N张
3. 碰/杠后没让玩家出牌→手牌只减不补
4. 显示只展示手牌不展示暴露副露

修复:
- 重构StepTurn: 先处理LastDiscard反应(碰/杠/胡)
  没人反应才摸牌→决定→出牌
- RemoveAll→Remove 精准删除
- 碰/杠后强制出一张牌
- HandleDiscardReactions替代旧CheckReactions
- RenderFinal展示Exposed副露

Demo/Program.cs

@@ -181,12 +181,19 @@ void RenderFinal(MahjongRoom room)
     Console.WriteLine($"  游戏结束，牌墙剩余 {state.Deck.Count} 张");
 
     Console.WriteLine();
-    Console.WriteLine("  最终手牌:");
+    Console.WriteLine("  最终状态:");
     foreach (var p in state.PlayerOrder)
     {
         var hand = state.Hands[p];
         var sorted = string.Join(", ", hand.OrderBy(t => t).Select(MahjongTile.ToString));
-        Console.WriteLine($"    {p}{(p == state.Dealer ? "(庄)" : "")}: {sorted} ({hand.Count}张)");
+        var exposedStr = "";
+        if (state.Exposed.TryGetValue(p, out var melds) && melds.Count > 0)
+        {
+            var meldDescs = melds.Select(m =>
+                $"{m.Type}[{string.Join(",", m.Tiles.Select(MahjongTile.ToString))}]");
+            exposedStr = $" | 已碰/杠: {string.Join(" ", meldDescs)}";
+        }
+        Console.WriteLine($"    {p}{(p == state.Dealer ? "(庄)" : "")}: {sorted} ({hand.Count}张){exposedStr}");
     }
 
     if (state.HuPlayers.Count > 0)

RuleEngine/MahjongRoom.cs

@@ -113,33 +113,48 @@ public class MahjongRoom
     public List<GameEvent> StepTurn()
     {
         State.RecentEvents.Clear();
+        var player = State.CurrentPlayer;
 
-        // Draw card
+        // Phase 1: Check reactions to last discard BEFORE drawing
+        // (order: starting from next player after discarder, check each alive player)
+        if (State.LastDiscard.HasValue && State.LastDiscardPlayer != null)
+        {
+            bool reacted = HandleDiscardReactions(State.LastDiscard.Value);
+            if (reacted)
+            {
+                AdvancePlayer();
+                return State.RecentEvents;
+            }
+            // No reaction — clear LastDiscard, current player will draw
+            State.LastDiscard = null;
+            State.LastDiscardPlayer = null;
+        }
+
+        // Phase 2: Draw card
         if (State.Deck.Count > 0)
         {
             int drawn = State.Deck[^1];
             State.Deck.RemoveAt(State.Deck.Count - 1);
-            State.Hands[State.CurrentPlayer].Add(drawn);
-            State.AddEvent("draw", State.CurrentPlayer, drawn,
+            State.Hands[player].Add(drawn);
+            State.AddEvent("draw", player, drawn,
                 $"摸牌: {MahjongTile.ToString(drawn)}");
 
             // Check flower
             if (MahjongTile.IsFlower(drawn))
             {
                 State.FlowerReplaced++;
-                State.AddEvent("flower_drawn", State.CurrentPlayer, drawn,
+                State.AddEvent("flower_drawn", player, drawn,
                     $"花牌 {MahjongTile.ToString(drawn)} → 补牌");
-                // Flower into flower pool and draw again
-                if (!State.FlowerPool.ContainsKey(State.CurrentPlayer))
-                    State.FlowerPool[State.CurrentPlayer] = new List<int>();
-                State.FlowerPool[State.CurrentPlayer].Add(drawn);
-                State.Hands[State.CurrentPlayer].Remove(drawn);
+                if (!State.FlowerPool.ContainsKey(player))
+                    State.FlowerPool[player] = new List<int>();
+                State.FlowerPool[player].Add(drawn);
+                State.Hands[player].Remove(drawn);
                 if (State.Deck.Count > 0)
                 {
                     int extra = State.Deck[^1];
                     State.Deck.RemoveAt(State.Deck.Count - 1);
-                    State.Hands[State.CurrentPlayer].Add(extra);
-                    State.AddEvent("draw", State.CurrentPlayer, extra,
+                    State.Hands[player].Add(extra);
+                    State.AddEvent("draw", player, extra,
                         $"补牌: {MahjongTile.ToString(extra)}");
                 }
             }
@@ -149,7 +164,6 @@ public class MahjongRoom
             State.IsDeckExhausted = true;
             State.AddEvent("deck_exhausted", "", null, "牌墙耗尽");
 
-            // Blood war: check ting and hua zhu
             if (_rules.Phases.Any(p => p.ParallelElimination))
             {
                 CheckHuaZhu();
@@ -159,12 +173,9 @@ public class MahjongRoom
             return State.RecentEvents;
         }
 
-        // Get legal actions for current player
-        var player = State.CurrentPlayer;
+        // Phase 3: Player decides what to do with their drawn hand
         bool requireWinFan = _rules.WinMinFan > 0;
         var legalActions = _phaseMachine.GetLegalActions(State, player, requireWinFan);
-
-        // AI decides
         var (action, tile) = _ais.First(a => a.Name == player).Decide(legalActions, State);
 
         if (action == "win")
@@ -177,7 +188,6 @@ public class MahjongRoom
 
             if (_rules.Phases.Any(p => p.ParallelElimination))
             {
-                // Blood war: continue without the winner
                 if (State.AlivePlayers.Count <= 1)
                 {
                     Settle();
@@ -199,46 +209,29 @@ public class MahjongRoom
             State.DiscardPool.Add(tile.Value);
             State.AddEvent("discard", player, tile.Value,
                 $"出牌: {MahjongTile.ToString(tile.Value)}");
-
-            // Check others' reactions (pung/kong/win)
-            bool reactionTaken = CheckReactions(tile.Value);
-            if (reactionTaken)
-            {
-                AdvancePlayer();
-                return State.RecentEvents;
-            }
-        }
-        else if (action == "pung")
-        {
-            // Handle pung
-            if (State.LastDiscard.HasValue)
-            {
-                int t = State.LastDiscard.Value;
-                State.Hands[player].RemoveAll(x => x == t);
-                State.Hands[player].RemoveAll(x => x == t);
-                State.LastDiscard = null;
-                State.Exposed[player].Add(new Meld
-                {
-                    Type = "pung",
-                    Tiles = new List<int> { t, t, t },
-                    SourcePlayer = State.LastDiscardPlayer ?? ""
-                });
-                State.AddEvent("pung", player, t, $"碰！{MahjongTile.ToString(t)}");
-            }
         }
 
         AdvancePlayer();
         return State.RecentEvents;
     }
 
-    private bool CheckReactions(int discardTile)
+    /// <summary>
+    /// Let other players react to a discard (pung/kong/win).
+    /// Returns true if someone reacted (turn passes to them).
+    /// </summary>
+    private bool HandleDiscardReactions(int discardTile)
     {
-        // Collect all claims with their priorities
+        // Collect claims from all alive players except the discarder
         var claims = new List<(string player, int priority, string action)>();
-        
-        foreach (var p in State.AlivePlayers)
+        string discarder = State.LastDiscardPlayer ?? "";
+
+        // Check in player order (starting after discarder)
+        int startIdx = State.PlayerOrder.IndexOf(discarder);
+        for (int offset = 1; offset < State.PlayerOrder.Count; offset++)
         {
-            if (p == State.CurrentPlayer) continue;
+            string p = State.PlayerOrder[(startIdx + offset) % State.PlayerOrder.Count];
+            if (!State.AlivePlayers.Contains(p)) continue;
+            if (p == discarder) continue;
 
             var handWithTile = new List<int>(State.Hands[p]) { discardTile };
             var winResult = _solver.CheckWin(handWithTile);
@@ -255,22 +248,22 @@ public class MahjongRoom
 
         if (claims.Count == 0) return false;
 
-        // Highest-priority claim wins
+        // Highest-priority claim wins (for simplicity: first highest wins)
         var best = claims.OrderByDescending(c => c.priority).First();
+        string bp = best.player;
 
         if (best.action == "win")
         {
             var winResult = _solver.CheckWin(
-                new List<int>(State.Hands[best.player]) { discardTile });
-            
-            State.HuPlayers.Add(best.player);
-            State.AlivePlayers.Remove(best.player);
-            State.AddEvent("win", best.player, discardTile,
+                new List<int>(State.Hands[bp]) { discardTile });
+            State.HuPlayers.Add(bp);
+            State.AlivePlayers.Remove(bp);
+            State.AddEvent("win", bp, discardTile,
                 $"胡！{MahjongTile.ToString(discardTile)}");
 
             if (!_rules.Phases.Any(ph => ph.ParallelElimination))
             {
-                _scoreEngine.Settle(State, best.player, winResult!, isSelfDraw: false);
+                _scoreEngine.Settle(State, bp, winResult!, isSelfDraw: false);
                 IsFinished = true;
             }
             return true;
@@ -278,21 +271,39 @@ public class MahjongRoom
 
         if (best.action == "pung" || best.action == "ming_kong")
         {
-            State.Hands[best.player].RemoveAll(t => t == discardTile);
-            State.Hands[best.player].RemoveAll(t => t == discardTile);
-            if (best.action == "ming_kong")
-                State.Hands[best.player].RemoveAll(t => t == discardTile);
-            
-            State.Exposed[best.player].Add(new Meld
+            // Remove tiles from hand (pung: 2, ming_kong: 3)
+            // The discard tile is taken from pool, not from hand
+            int toRemove = best.action == "ming_kong" ? 3 : 2;
+            for (int r = 0; r < toRemove; r++)
+                State.Hands[bp].Remove(discardTile);
+
+            // Create exposed meld
+            int meldSize = best.action == "ming_kong" ? 4 : 3;
+            var meldTiles = Enumerable.Repeat(discardTile, meldSize).ToList();
+            State.Exposed[bp].Add(new Meld
             {
                 Type = best.action,
-                Tiles = new List<int> { discardTile, discardTile, discardTile,
-                    discardTile },  // 4th for kong
-                SourcePlayer = State.CurrentPlayer
+                Tiles = meldTiles,
+                SourcePlayer = discarder
             });
-            State.CurrentPlayer = best.player;
+            State.CurrentPlayer = bp;
             State.LastDiscard = null;
-            State.AddEvent(best.action, best.player, discardTile, best.action == "pung" ? "碰！" : "明杠！");
+            State.LastDiscardPlayer = null;
+            State.AddEvent(best.action, bp, discardTile,
+                best.action == "pung" ? "碰！" : "明杠！");
+
+            // After pung/kong, the reacting player must discard a tile
+            var hand = State.Hands[bp];
+            if (hand.Count > 0)
+            {
+                int tileToDiscard = hand[Random.Shared.Next(hand.Count)];
+                State.Hands[bp].Remove(tileToDiscard);
+                State.LastDiscard = tileToDiscard;
+                State.LastDiscardPlayer = bp;
+                State.DiscardPool.Add(tileToDiscard);
+                State.AddEvent("discard", bp, tileToDiscard,
+                    $"出牌: {MahjongTile.ToString(tileToDiscard)}");
+            }
             return true;
         }