start of draft option upgrades

Assets/_Project/Scripts/Gameplay/BuilderUpgradeManager.cs

@@ -20,8 +20,9 @@ namespace TD.Gameplay
     /// same constraint on a struct); <c>byte</c> already does, for free.</para>
     ///
     /// <para><b>Granted via draft.</b> <see cref="TD.Gameplay.Draft.BuilderEffectDraftOption"/>
-    /// calls <see cref="ServerGrantEffect"/> when a player picks it. Effects are permanent for
-    /// the match — there is no revoke.</para>
+    /// calls <see cref="ServerGrantEffect"/> when a player picks it. Effects are otherwise
+    /// permanent for the match — the only way one leaves the granted set is
+    /// <see cref="ServerUpgradeEffect"/> swapping it for its upgraded replacement.</para>
     ///
     /// <para><b>Query, don't snapshot.</b> Consumers (e.g. <see cref="WaveManager"/> awarding
     /// kill gold) query this manager live at the point of use rather than towers caching their
@@ -117,5 +118,24 @@ namespace TD.Gameplay
             grantedKinds.Add(value);
             return true;
         }
+
+        /// <summary>
+        /// Server-only: replaces a previously granted effect with a different one (an upgrade
+        /// pick). No-op if the old effect isn't currently granted or the new one already is.
+        /// Returns true if the swap happened.
+        /// </summary>
+        public bool ServerUpgradeEffect(BuilderEffectKind oldKind, BuilderEffectKind newKind)
+        {
+            if (!IsServer) return false;
+
+            byte newValue = (byte)newKind;
+            if (grantedKinds.Contains(newValue)) return false;
+
+            byte oldValue = (byte)oldKind;
+            if (!grantedKinds.Remove(oldValue)) return false;
+
+            grantedKinds.Add(newValue);
+            return true;
+        }
     }
 }