fixed the encounter window

Runtime/EncounterTable.cs

@@ -42,5 +42,34 @@ namespace Jovian.EncounterSystem {
 
             return pool[UnityEngine.Random.Range(0, pool.Count)];
         }
+
+#if UNITY_EDITOR
+        // Unity's inspector "+" duplicates the previous list element, including nested internalId
+        // GUIDs. Regenerate any duplicates so every encounter carries a unique internalId.
+        private void OnValidate() {
+            if(encounters == null) {
+                return;
+            }
+
+            var seen = new HashSet<string>();
+            var changed = false;
+            foreach(var encounter in encounters) {
+                if(encounter?.EncounterDefinition == null) {
+                    continue;
+                }
+
+                var id = encounter.EncounterDefinition.internalId;
+                if(string.IsNullOrEmpty(id) || !seen.Add(id)) {
+                    encounter.EncounterDefinition.internalId = Guid.NewGuid().ToString();
+                    seen.Add(encounter.EncounterDefinition.internalId);
+                    changed = true;
+                }
+            }
+
+            if(changed) {
+                UnityEditor.EditorUtility.SetDirty(this);
+            }
+        }
+#endif
     }
 }