new builder option per draft - first one is gold per kill

Assets/_Project/Scripts/Gameplay/BuilderEffects/BuilderEffectPool.cs

@@ -0,0 +1,66 @@
+// Assets/_Project/Scripts/Gameplay/BuilderEffects/BuilderEffectPool.cs
+using System;
+using UnityEngine;
+using TD.Core;
+
+namespace TD.Gameplay.BuilderEffects
+{
+    /// <summary>
+    /// Scene singleton holding every <see cref="BuilderEffectDefinition"/> available this match,
+    /// authored as a flat array in the inspector for convenience. Internally it builds a
+    /// fixed-size table indexed by <see cref="BuilderEffectKind"/> so lookups are a single array
+    /// access, not a scan.
+    /// </summary>
+    /// <remarks>
+    /// Plain MonoBehaviour: identical on every peer (same assets), so there is nothing to sync.
+    /// The server reads it to resolve grants; clients read it to render an "active effects" list.
+    /// </remarks>
+    public class BuilderEffectPool : MonoBehaviour
+    {
+        public static BuilderEffectPool Instance { get; private set; }
+
+        [Tooltip("Every BuilderEffectDefinition asset available this match. One entry per " +
+                 "BuilderEffectKind — order doesn't matter, Kind on the asset itself decides " +
+                 "its slot.")]
+        [SerializeField] private BuilderEffectDefinition[] effects;
+
+        // Fixed-size, enum-indexed lookup built once in Awake. Sized to the enum's entry count,
+        // not authored count, so an out-of-range Kind is a compile-time impossibility rather
+        // than a bounds check we'd otherwise need on every Get().
+        private BuilderEffectDefinition[] byKind;
+
+        private void Awake()
+        {
+            if (Instance != null && Instance != this)
+            {
+                Debug.LogError("[BuilderEffectPool] Multiple instances detected. Only one per scene.");
+                return;
+            }
+            Instance = this;
+
+            int kindCount = Enum.GetValues(typeof(BuilderEffectKind)).Length;
+            byKind = new BuilderEffectDefinition[kindCount];
+            if (effects == null) return;
+
+            for (int i = 0; i < effects.Length; i++)
+            {
+                var def = effects[i];
+                if (def == null) continue;
+                byKind[(int)def.Kind] = def;
+            }
+        }
+
+        private void OnDestroy()
+        {
+            if (Instance == this) Instance = null;
+        }
+
+        /// <summary>Returns the effect asset for <paramref name="kind"/>, or null if none is
+        /// authored in this pool.</summary>
+        public BuilderEffectDefinition Get(BuilderEffectKind kind)
+        {
+            int i = (int)kind;
+            return (byKind != null && i >= 0 && i < byKind.Length) ? byKind[i] : null;
+        }
+    }
+}