diff -r 48c4eec2b7e6 -r 8c2e4d02f4ef wp/wp-admin/includes/class-core-upgrader.php
--- a/wp/wp-admin/includes/class-core-upgrader.php	Fri Sep 05 18:40:08 2025 +0200
+++ b/wp/wp-admin/includes/class-core-upgrader.php	Fri Sep 05 18:52:52 2025 +0200
@@ -13,6 +13,10 @@
  * It allows for WordPress to upgrade itself in combination with
  * the wp-admin/includes/update-core.php file.
  *
+ * Note: Newly introduced functions and methods cannot be used here.
+ * All functions must be present in the previous version being upgraded from
+ * as this file is used there too.
+ *
  * @since 2.8.0
  * @since 4.6.0 Moved to its own file from wp-admin/includes/class-wp-upgrader.php.
  *