docs: explain match assertions and annotation type distinctions

crates/core/tests/runtime.rs

@@ -164,6 +164,7 @@ fn explicit_references_control_lifetime_and_copies_are_borrowed() {
     vm.release(owned).unwrap();
     assert_eq!(drops.load(Ordering::SeqCst), 1);
     assert_eq!(vm.object_count(), 0);
+    // 最后拥有根释放后，复制来的借用句柄必须失效，不能当作额外拥有根。
     assert!(matches!(vm.object(borrowed), Err(VmError::InvalidHandle)));
     assert_eq!(vm.release(borrowed), Err(VmError::InvalidHandle));
 }
@@ -210,6 +211,7 @@ fn replacing_the_same_edge_does_not_destroy_the_target() {
     assert_eq!(vm.ref_count(target).unwrap(), 1);
     vm.set_attr(owner, "child", Value::Number(7_i64.into()))
         .unwrap();
+    // 属性从对象改为数值会归还原目标最后的边，因此旧 target 句柄应失效。
     assert!(matches!(vm.object(target), Err(VmError::InvalidHandle)));
     assert_eq!(
         vm.get_attr(owner, "child").unwrap(),
@@ -350,7 +352,9 @@ fn cycles_remain_while_rooted_and_are_collected_when_unreachable() {
     assert_eq!(vm.collect_cycles(), 2);
     assert_eq!(vm.collect_cycles(), 0);
     assert_eq!(drops.load(Ordering::SeqCst), 2);
+    // 无根环回收后第一个旧句柄失效，不能只依赖析构计数判断槽是否仍可访问。
     assert!(matches!(vm.object(first), Err(VmError::InvalidHandle)));
+    // 同一垃圾环中的第二个对象也必须失效，避免只回收部分环。
     assert!(matches!(vm.object(second), Err(VmError::InvalidHandle)));
 }