fix: defineProperty 纯属性描述符按 ES 规范默认创建 value=undefined，不再错误抛 TypeError

crates/oxide_builtins/src/object.rs

@@ -287,10 +287,13 @@ pub fn object_define_property<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResul
         }
     } else {
         if existing_pos.is_none() {
-            return NativeResult::Err(crate::error::create_type_error(
-                vm,
-                "Cannot define new property without value or accessor",
-            ));
+            if vm
+                .define_data_property(obj, si, JsValue::undefined(), PropAttributes::new(false, enumerable, configurable))
+                .is_err()
+            {
+                return NativeResult::Err(crate::error::create_type_error(vm, "Cannot define property"));
+            }
+            return NativeResult::Ok(obj_val);
         }
         let is_accessor = existing_meta.map(|m| m.is_accessor).unwrap_or(false);
         let writable = existing_meta.map(|m| m.attributes.writable()).unwrap_or(true);

crates/oxide_vm/tests/define_property_descriptor_tests.rs

@@ -92,11 +92,11 @@ fn get_own_property_descriptor_accessor_fields() {
     );
 }
 
-// -- New property without value or accessor throws --
+// -- New property without value or accessor defaults to data descriptor (ES spec behavior) --
 #[test]
-fn define_property_new_without_value_throws() {
-    let result = eval_str("var obj={}; Object.defineProperty(obj,'x',{enumerable:true})");
-    assert_err_contains(result, "Cannot define new property without value or accessor");
+fn define_property_new_attributes_only_defaults_value_undefined() {
+    let r = eval_str("var obj={}; Object.defineProperty(obj,'x',{enumerable:true}); obj.x").unwrap();
+    assert!(r.is_undefined(), "new prop with only enumerable should default value to undefined, got {:?}", r);
 }
 
 // -- Partial configurable on existing property preserves value --