fix slow area spell area of effect

Assets/_Project/Scripts/Gameplay/BuilderSpells/SlowAreaZone.cs

@@ -0,0 +1,77 @@
+// Assets/_Project/Scripts/Gameplay/BuilderSpells/SlowAreaZone.cs
+using UnityEngine;
+using TD.Core;
+
+namespace TD.Gameplay.BuilderSpells
+{
+    /// <summary>
+    /// Server-only, non-networked lingering area spawned by
+    /// <see cref="SlowAreaSpellDefinition.ServerCast"/>. Re-scans its radius on an
+    /// interval for its lifetime and keeps refreshing the slow on anything standing
+    /// inside, so enemies get slowed as they walk through rather than only at the
+    /// instant of cast.
+    /// </summary>
+    /// <remarks>
+    /// Never spawned as a <see cref="Unity.Netcode.NetworkObject"/> — it runs
+    /// server-side only, and the slow it applies already reaches clients through
+    /// <see cref="EnemyStatus"/>'s own NetworkVariable, the same as an instant hit.
+    /// </remarks>
+    public class SlowAreaZone : MonoBehaviour
+    {
+        private const float TickInterval = 0.2f;
+
+        private float radius;
+        private float slowFactor;
+        private float effectDuration;
+        private LayerMask enemyLayerMask;
+        private PlayerSlot owner;
+
+        private readonly Collider[] overlapBuffer = new Collider[64];
+        private float tickTimer;
+
+        public static SlowAreaZone Spawn(Vector3 position, float radius, float slowFactor,
+            float effectDuration, LayerMask enemyLayerMask, PlayerSlot owner)
+        {
+            var zoneObject = new GameObject("SlowAreaZone (Server)");
+            zoneObject.transform.position = position;
+
+            var zone = zoneObject.AddComponent<SlowAreaZone>();
+            zone.radius = radius;
+            zone.slowFactor = slowFactor;
+            zone.effectDuration = effectDuration;
+            zone.enemyLayerMask = enemyLayerMask;
+            zone.owner = owner;
+            zone.ApplyToOverlapping();
+
+            Destroy(zoneObject, effectDuration);
+            return zone;
+        }
+
+        private void Update()
+        {
+            tickTimer -= Time.deltaTime;
+            if (tickTimer > 0f) return;
+
+            ApplyToOverlapping();
+        }
+
+        private void ApplyToOverlapping()
+        {
+            tickTimer = TickInterval;
+
+            int count = Physics.OverlapSphereNonAlloc(
+                transform.position, radius, overlapBuffer, enemyLayerMask);
+
+            for (int i = 0; i < count; i++)
+            {
+                var enemyHealth = overlapBuffer[i].GetComponent<EnemyHealth>();
+                if (enemyHealth == null || enemyHealth.IsDead) continue;
+
+                var enemyStatus = overlapBuffer[i].GetComponent<EnemyStatus>();
+                if (enemyStatus == null) continue;
+
+                enemyStatus.ApplyEffect(DamageType.Cold, slowFactor, effectDuration, owner);
+            }
+        }
+    }
+}