Media: Fix incorrect count and lingering thumbnail in the media modal

[i-am-chitti]

Trac ticket: https://core.trac.wordpress.org/ticket/65513

Fixes two issues in the media library modal (reproducible on a real server; masked on WordPress Playground because the delete request resolves almost instantly there).

Bug 1 — wrong count on first upload

After uploading the first image into an empty library through the Featured Image modal, the Media Library tab read "Showing 1 of 2 media items" instead of "1 of 1".

Attachments.observe() bound the total-count handlers (_addToTotalAttachments / _removeFromTotalAttachments) to every observed collection. The Featured Image state also observes the selection (library.observe( this.get('selection') )), so with autoSelect an uploaded image is added to both the mirrored query and the selection, and was counted twice.

The counters are now bound only when the observed collection is the mirrored query (attachments === this.mirroring), so the total reflects the library itself. This also resolves the same latent double-count in the replace-image, gallery-edit, and collection-edit states.

Bug 2 — deleted image lingers in the grid

After "Delete permanently" in the modal, the deleted attachment stayed visible in the Media Library grid (and remained the selected featured image), even though the query and global collections dropped it correctly.

"Delete permanently" destroys the model with { wait: true }, so Backbone fires the destroy event from its AJAX success callback — which runs before the delete request's own .done() handler, where this.destroyed = true was being set. During the destroy cascade the model therefore still validated as not destroyed, and the mirrored library collection re-added it via validate(). The flag is now set before the request (and restored on failure), so aggregate collections filter the attachment out the moment destroy fires. This is deterministic, not a race — the leftover item is stable until a re-query/reload.

Also

• Corrects two inline-doc issues in the touched code: a missing @param name on observe() and a copy/paste description on _removeFromTotalAttachments().
• Adds an end-to-end test (tests/e2e/specs/featured-image-modal.test.js) covering both the count and the deletion. It passes with these changes and fails without them.

Not included

A related symptom — after deleting the attachment, the block editor's sidebar still shows it as the featured image — lives in the block editor's data store (core/editor), whose source is in the Gutenberg repository rather than this one. Here it is - WordPress/gutenberg#79820

Testing

1. Start with an empty Media Library.
2. Edit a post, open the Featured Image modal, and upload one image on the Upload files tab.
3. Switch to the Media Library tab → the count should read "Showing 1 of 1 media items".
4. With the uploaded image selected, click Delete permanently and confirm → the image should disappear from the grid.

Screenshots

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 4.8
Used for: Ticket analysis, root-cause investigation, and the end-to-end test. All changes were reviewed.

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