start of draft option upgrades

Assets/_Project/Scripts/Gameplay/Draft/BuilderSpellUpgradeDraftOption.cs

@@ -0,0 +1,52 @@
+// Assets/_Project/Scripts/Gameplay/Draft/BuilderSpellUpgradeDraftOption.cs
+using UnityEngine;
+using TD.Core;
+using TD.Gameplay.BuilderSpells;
+
+namespace TD.Gameplay.Draft
+{
+    /// <summary>
+    /// Draft choice — "upgrade a builder spell you already have". Replaces
+    /// <see cref="BaseKind"/> with <see cref="UpgradedKind"/> in the player's
+    /// <see cref="PlayerSpellLoadout"/>, in place — the upgraded spell keeps the same hotkey
+    /// slot the base spell occupied.
+    /// </summary>
+    /// <remarks>
+    /// Mirrors <see cref="BuilderSpellDraftOption"/>, but swaps rather than adds (so it doesn't
+    /// consume a slot). Only offered while the player currently has <see cref="BaseKind"/>
+    /// granted — once taken, <see cref="BaseKind"/> is removed, which automatically makes this
+    /// option (and any sibling upgrade branching off the same base) invalid for future drafts.
+    /// </remarks>
+    [CreateAssetMenu(fileName = "BuilderSpellUpgradeOption",
+                      menuName = "TD/Draft/Builder Spell Upgrade Option")]
+    public class BuilderSpellUpgradeDraftOption : DraftOption
+    {
+        [Header("Payload")]
+        [Tooltip("The builder spell this option upgrades from.")]
+        public BuilderSpellKind BaseKind;
+
+        [Tooltip("The builder spell this option upgrades to.")]
+        public BuilderSpellKind UpgradedKind;
+
+        public override bool IsValidFor(ulong clientId)
+        {
+            var loadout = PlayerSpellLoadout.GetForClient(clientId);
+            return loadout != null && loadout.PlayerHasSpell(BaseKind);
+        }
+
+        public override bool ServerApply(ulong clientId)
+        {
+            var loadout = PlayerSpellLoadout.GetForClient(clientId);
+            return loadout != null && loadout.ServerUpgradeSpell(BaseKind, UpgradedKind);
+        }
+
+        /// <summary>Inherits the upgraded spell's icon (resolved from the pool by
+        /// <see cref="UpgradedKind"/>) unless this option assigns an override.</summary>
+        public override Sprite ResolveIcon()
+        {
+            if (Icon != null) return Icon;
+            var def = BuilderSpellPool.Instance != null ? BuilderSpellPool.Instance.Get(UpgradedKind) : null;
+            return def != null ? def.Icon : null;
+        }
+    }
+}