fix(api): avoid rebuilding dealer defaults during spawn

Cache built dealer defaults when they are registered and use that cached
configuration when wiring recommendation hooks at runtime.

This prevents unrelated dealer default callbacks from being re-executed for
third-party NPCs during spawn, which was causing null reference failures on
NPCs that did not actually use recommendation defaults.

Author: ifBars

S1API/Entities/NPC.cs

@@ -118,6 +118,7 @@ public abstract class NPC : Saveable, IEntity, IHealth
         internal static readonly System.Collections.Generic.Dictionary<System.Type, System.Action<NPCRelationshipDataBuilder>> TypeToRelationshipDefaults = new System.Collections.Generic.Dictionary<System.Type, System.Action<NPCRelationshipDataBuilder>>();
         private static readonly System.Collections.Generic.Dictionary<System.Type, System.Action<RandomInventoryItemsBuilder>> TypeToRandomInventoryDefaults = new System.Collections.Generic.Dictionary<System.Type, System.Action<RandomInventoryItemsBuilder>>();
         private static readonly System.Collections.Generic.Dictionary<System.Type, System.Action<DealerDataBuilder>> TypeToDealerDefaults = new System.Collections.Generic.Dictionary<System.Type, System.Action<DealerDataBuilder>>();
+        private static readonly System.Collections.Generic.Dictionary<System.Type, DealerDataBuilder.DealerConfigData> TypeToBuiltDealerDefaults = new System.Collections.Generic.Dictionary<System.Type, DealerDataBuilder.DealerConfigData>();
         private static readonly System.Collections.Generic.Dictionary<System.Type, (Vector3 position, Quaternion rotation)> TypeToSpawnPosition = new System.Collections.Generic.Dictionary<System.Type, (Vector3, Quaternion)>();
         private static readonly System.Collections.Generic.HashSet<System.Type> CustomerTypes = new System.Collections.Generic.HashSet<System.Type>();
         private static readonly System.Collections.Generic.HashSet<System.Type> DealerTypes = new System.Collections.Generic.HashSet<System.Type>();
@@ -927,7 +928,20 @@ internal static void RegisterDealerDefaultsForType(System.Type npcType, System.A
         {
             if (npcType == null || configure == null)
                 return;
+
             TypeToDealerDefaults[npcType] = configure;
+
+            try
+            {
+                var builder = new DealerDataBuilder();
+                configure(builder);
+                TypeToBuiltDealerDefaults[npcType] = builder.BuildInternal();
+            }
+            catch (Exception ex)
+            {
+                TypeToBuiltDealerDefaults.Remove(npcType);
+                Logger.Warning($"[S1API] Failed to cache dealer defaults for '{npcType.Name}': {ex.Message}");
+            }
         }
 
         internal static void RegisterDealerType(System.Type npcType)
@@ -959,14 +973,33 @@ internal static System.Action<DealerDataBuilder> GetDealerDefaultsForType(System
             return cfg;
         }
 
+        internal static DealerDataBuilder.DealerConfigData GetBuiltDealerDefaultsForType(System.Type npcType)
+        {
+            if (npcType == null)
+                return null;
+
+            TypeToBuiltDealerDefaults.TryGetValue(npcType, out var cfg);
+            return cfg;
+        }
+
         internal static DealerDataBuilder.DealerConfigData BuildDealerDefaultsForType(System.Type npcType)
         {
+            var cached = GetBuiltDealerDefaultsForType(npcType);
+            if (cached != null)
+                return cached;
+
             var cfg = GetDealerDefaultsForType(npcType);
             if (cfg == null)
                 return null;
+
             var builder = new DealerDataBuilder();
             cfg(builder);
-            return builder.BuildInternal();
+            var built = builder.BuildInternal();
+
+            if (npcType != null)
+                TypeToBuiltDealerDefaults[npcType] = built;
+
+            return built;
         }
 
         internal static void RegisterRandomInventoryDefaultsForType(System.Type npcType, System.Action<RandomInventoryItemsBuilder> configure)
@@ -3075,13 +3108,14 @@ private static void CheckAndSetCustomNpcsReady()
 
         private void ApplyDealerRecommendationDefaults()
         {
-            if (!IsDealerType(GetType()))
+            var npcType = GetType();
+            if (!IsDealerType(npcType))
             {
                 ClearDealerRecommendationHooks();
                 return;
             }
 
-            var defaults = BuildDealerDefaultsForType(GetType());
+            var defaults = GetBuiltDealerDefaultsForType(npcType);
             if (defaults == null || defaults.Recommendations.Count == 0)
             {
                 ClearDealerRecommendationHooks();