start of draft option upgrades

Assets/_Project/Scripts/Gameplay/PlayerTowerDeck.cs

@@ -146,5 +146,30 @@ namespace TD.Gameplay
             unlockedTypeIds.Add(towerTypeId);
             return true;
         }
+
+        /// <summary>
+        /// Server-only: replaces a previously unlocked tower type with a different one (an
+        /// upgrade pick) — every tower of that type placed from now on uses the new definition.
+        /// Already-placed towers keep whatever type they were placed with; this only changes
+        /// what's placeable going forward. No-op if the old type isn't currently unlocked or
+        /// the new one already is. Returns true if the swap happened.
+        /// </summary>
+        public bool ServerUpgradeTower(int oldTypeId, int newTypeId)
+        {
+            if (!IsServer) return false;
+            if (newTypeId <= 0) return false;
+            if (Contains(newTypeId)) return false;
+
+            for (int i = 0; i < unlockedTypeIds.Count; i++)
+            {
+                if (unlockedTypeIds[i] == oldTypeId)
+                {
+                    unlockedTypeIds.RemoveAt(i);
+                    unlockedTypeIds.Add(newTypeId);
+                    return true;
+                }
+            }
+            return false;
+        }
     }
 }