first pass at enemy upgrades

Assets/_Project/Scripts/Gameplay/EnemyAbilities/SplitOnDeathAbilityDefinition.cs

@@ -0,0 +1,40 @@
+// Assets/_Project/Scripts/Gameplay/EnemyAbilities/SplitOnDeathAbilityDefinition.cs
+using UnityEngine;
+using TD.Core;
+
+namespace TD.Gameplay.EnemyAbilities
+{
+    /// <summary>
+    /// On death, spawns <see cref="SplitCount"/> copies of <see cref="SplitInto"/> at the corpse's
+    /// position, continuing on toward the goal instead of restarting from the wave's spawner.
+    /// </summary>
+    [CreateAssetMenu(fileName = "SplitOnDeathAbility", menuName = "TD/Enemy Abilities/Split On Death")]
+    public class SplitOnDeathAbilityDefinition : EnemyAbilityDefinition
+    {
+        public override EnemyAbilityKind Kind => EnemyAbilityKind.SplitOnDeath;
+
+        [Header("Split")]
+        [Tooltip("Smaller enemy type spawned when this enemy dies.")]
+        public EnemyDefinition SplitInto;
+
+        [Tooltip("How many copies of SplitInto spawn on death.")]
+        [Min(1)]
+        public int SplitCount = 2;
+
+        [Tooltip("Random scatter radius (world units) applied to each split spawn so they don't " +
+                 "spawn exactly on top of each other.")]
+        [Min(0f)]
+        public float ScatterRadius = 0.5f;
+
+        public override void ServerOnDeath(EnemyAbility instance, EnemyHealth health)
+        {
+            if (SplitInto == null) return;
+
+            var movement = instance.GetComponent<EnemyMovement>();
+            var atTile = GridCoordinates.WorldToGrid(instance.transform.position);
+            var ownerSlot = movement != null ? movement.OriginZone : PlayerSlot.None;
+
+            WaveManager.Instance?.ServerSpawnSplitEnemies(SplitInto, SplitCount, atTile, ownerSlot, ScatterRadius);
+        }
+    }
+}