first pass at enemy upgrades

Assets/_Project/Scripts/Gameplay/EnemyAbility.cs

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+// Assets/_Project/Scripts/Gameplay/EnemyAbility.cs
+using Unity.Netcode;
+using UnityEngine;
+using TD.Core;
+using TD.Gameplay.EnemyAbilities;
+
+namespace TD.Gameplay
+{
+    /// <summary>
+    /// Per-enemy ability slot. Holds the <see cref="EnemyAbilityDefinition"/> rolled for this
+    /// instance (if any) and drives its server-only hooks.
+    /// </summary>
+    /// <remarks>
+    /// <b>Initialization:</b> Call <see cref="InitializeServer"/> on the server immediately after
+    /// <c>Instantiate</c> and before <c>NetworkObject.Spawn()</c>, following the same pattern as
+    /// <c>EnemyHealth.InitializeServer</c> / <c>EnemyMovement.InitializeServer</c>.
+    ///
+    /// <b>Optional component:</b> Not required by <c>EnemyHealth</c> or <c>EnemyMovement</c> —
+    /// <c>WaveManager.SpawnEnemy</c> only rolls and assigns an ability when this component is
+    /// present on the prefab, so existing enemy prefabs are unaffected until it's added to them.
+    ///
+    /// <b>On-death hook is not event-driven:</b> <c>WaveManager.HandleEnemyKilled</c> calls
+    /// <see cref="EnemyAbilityDefinition.ServerOnDeath"/> directly (via <see cref="Definition"/>)
+    /// rather than this component subscribing to <c>EnemyHealth.OnDied</c> itself — that keeps a
+    /// split-spawn's <c>activeEnemyCount</c> increment ordered before the triggering kill's
+    /// decrement, regardless of NetworkBehaviour subscription order.
+    /// </remarks>
+    [RequireComponent(typeof(NetworkObject))]
+    public class EnemyAbility : NetworkBehaviour
+    {
+        private readonly NetworkVariable<byte> kind = new NetworkVariable<byte>(
+            (byte)EnemyAbilityKind.None,
+            NetworkVariableReadPermission.Everyone,
+            NetworkVariableWritePermission.Server);
+
+        // ----- Pre-spawn init (server-local) ----------------------------------
+
+        private EnemyAbilityDefinition pendingDefinition;
+        private bool                   hasPendingInit;
+
+        // ----- Public state -----------------------------------------------------
+
+        /// <summary>The ability rolled for this enemy, or null if none was rolled.</summary>
+        public EnemyAbilityDefinition Definition { get; private set; }
+
+        /// <summary>Replicated kind of the rolled ability. <see cref="EnemyAbilityKind.None"/> if
+        /// none was rolled.</summary>
+        public EnemyAbilityKind Kind => (EnemyAbilityKind)kind.Value;
+
+        // ----- Server-only pre-spawn init -------------------------------------
+
+        /// <summary>
+        /// Called by <c>WaveManager</c> on the server after <c>Instantiate</c> and before
+        /// <c>NetworkObject.Spawn()</c>. <paramref name="definition"/> may be null, meaning no
+        /// ability was rolled for this enemy.
+        /// </summary>
+        public void InitializeServer(EnemyAbilityDefinition definition)
+        {
+            pendingDefinition = definition;
+            hasPendingInit    = true;
+        }
+
+        // ----- NGO lifecycle --------------------------------------------------
+
+        public override void OnNetworkSpawn()
+        {
+            if (!IsServer || !hasPendingInit) return;
+
+            Definition     = pendingDefinition;
+            kind.Value     = (byte)(Definition != null ? Definition.Kind : EnemyAbilityKind.None);
+            hasPendingInit = false;
+
+            Definition?.ServerOnSpawn(this);
+        }
+
+        // ----- Server tick ------------------------------------------------
+
+        private void Update()
+        {
+            if (!IsServer || Definition == null) return;
+            Definition.ServerTick(this, Time.deltaTime);
+        }
+    }
+}