第十阶段 stage 1（二）：永续合约单仓位、保证金金额一行、名义价值

src/Decentralized.Domain/Perps.cs

@@ -22,7 +22,7 @@ namespace Decentralized.Domain
             : (Margin + Size * Entry) / (Size * (1 + Tuning.PerpMaint));
     }
 
-    public enum PerpResult { Ok, Banned, Debt, Leverage, Size, Funds, Opposite, NoPosition, Margin, Thin }
+    public enum PerpResult { Ok, Banned, Debt, Leverage, Size, Funds, Opposite, NoPosition, Margin, Thin, Single }
 
     /// <summary>夜间发生的事：强平、自动减仓、催收没收、核销。</summary>
     public sealed class PerpEvent
@@ -73,7 +73,7 @@ namespace Decentralized.Domain
             return total > 0 ? Math.Min(1, amount * price(Assets.CRC) / total) : 0;
         }
 
-        /// <summary>开仓或加仓（同方向）：保证金 + 手续费从账户的 CRC 里扣，污点与成本按保证金的价值比例随保证金进仓位。</summary>
+        /// <summary>开仓（同一时间只有一个仓位，已有仓位时只能 <see cref="AddMargin"/>）：保证金 + 手续费从账户的 CRC 里扣，污点与成本按保证金的价值比例随保证金进仓位。</summary>
         public PerpResult Open(Wallet acct, string product, bool isLong, double margin, int leverage, double price, int day, Func<string, double> pr)
         {
             if (Banned(day)) return PerpResult.Banned;
@@ -82,6 +82,7 @@ namespace Decentralized.Domain
             if (margin <= 0 || price <= 0) return PerpResult.Margin;
             var pos = Of(product);
             if (pos != null && pos.Long != isLong) return PerpResult.Opposite;
+            if (Positions.Count > 0) return PerpResult.Single;   // 只支持逐仓、一个仓位：有仓位后只能追加保证金
             double notional = margin * leverage, fee = notional * Tuning.PerpFee;
             double spot = price;
             price = Exec(price, notional, isLong, day);