Fix some script bugs

types/asset/asseteventproxy.d.ts

@@ -0,0 +1,23 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+/**
+ * An event proxy with up to 4 subscribable callback slots (indices 0–3).
+ * Assign a function to subscribe; assign `null` to unsubscribe.
+ *
+ * @example
+ * assets.onLoaded[0] = () => { Console.print('all loaded'); };
+ * assets.onLoaded[0] = null; // unsubscribe
+ */
+interface AssetEventProxy {
+  0: (() => void) | null;
+  1: (() => void) | null;
+  2: (() => void) | null;
+  3: (() => void) | null;
+  /** Number of available slots (always 4). */
+  readonly length: number;
+}