upload.php (Media Library)

• URL: /wp-admin/upload.php
• Capability required: upload_files (and delete_post for deleting attachments).
• What it does: Lists media items, handles bulk actions, and provides entry points to edit attachments.
• Key hooks: handle_bulk_actions-{$screen}.

media.php (Deprecated media handler)

• URL: /wp-admin/media.php
• Capability required: None in file; defers to upload.php and will redirect.
• What it does: Deprecated action handler that redirects to upload.php for attachment editing.
• Key hooks: (none in file).

media-new.php (Add New Media)

• URL: /wp-admin/media-new.php
• Capability required: upload_files (and edit_post if attaching to a post).
• What it does: Uploads new media (plupload or browser uploader) and redirects to the Media Library.
• Key hooks: (none in file; standard admin header/footer hooks apply).

async-upload.php (Async upload handler)

• URL: /wp-admin/async-upload.php
• Capability required: upload_files (and edit_post when attaching to a post).
• What it does: Handles async uploads from Plupload or legacy uploaders, returns attachment HTML or ID.
• Key hooks: async_upload_{$type}.