first pass at enemy upgrades

Assets/_Project/Scripts/Gameplay/EnemyMovement.cs

@@ -73,6 +73,11 @@ namespace TD.Gameplay
         // the goal). Without this, every zone crossing was counted as a leak; only
         // the originating player should be credited a leak per the design.
         private PlayerSlot        originZone    = PlayerSlot.None;
+
+        /// <summary>The zone (player) this enemy was originally spawned for — see
+        /// <see cref="InitializeServer"/>. Used by on-death abilities (e.g. Split on Death) so
+        /// spawned children preserve the same leak attribution as their parent.</summary>
+        public PlayerSlot OriginZone => originZone;
         // Latches once the enemy has crossed its origin zone's leak volume, so we
         // never double-count a leak if the enemy re-enters its origin (rare but
         // possible if pathing is dynamic).