Critical error when setting Featured Image #74
Description
When saving after having selected a Featured Image, the following error appears in a black box at the bottom:
There has been a critical error on this website. Learn more about troubleshooting WordPress.
Root cause
The REST save endpoint (press_this_rest_save_post) calls side_load_images(), which internally uses media_sideload_image() from wp-admin/includes/media.php. REST API requests do not load wp-admin/includes/ files by default, so this call results in a PHP fatal error: "Call to undefined function media_sideload_image()".
The error surfaces when the post content contains <img> tags with external URLs (e.g. scraped images inserted via the media panel). The sideload endpoint already includes these admin files, but the save endpoint was missing them.
