ts is trying to narrow the type too hard

src/vm.ts

@@ -26,9 +26,7 @@ export class VM {
     this.scope = new Scope()
   }
 
-  registerFunction(name: string, fn: NativeFunction | Function) {
-    // If it's already a NativeFunction, use it directly
-    // Otherwise, assume it's a JS function and wrap it
+  registerFunction(name: string, fn: Function) {
     const wrapped = isWrapped(fn) ? fn as NativeFunction : wrapNative(fn)
     this.nativeFunctions.set(name, wrapped)
   }