Media: Correct attachment count in featured image modal.

[SwapnilWordpress]

Trac ticket: https://core.trac.wordpress.org/ticket/58729

Summary

Fixes incorrect "Showing X of Y media items" text in the media modal when uploading a featured image (and when using Replace featured image).

Problem

When setting a featured image from the post editor:

1. Open Posts → edit a post → Set featured image.
2. Upload a single image.
3. The footer shows "Showing 1 of 2 media items" instead of "Showing 1 of 1 media items".

The displayed count (X) is correct, but the total (Y) is inflated. The count can also look wrong when reopening the modal via Replace. Same class of bug as #55345 and #57488.

Root cause

The media library keeps a server-side total in totalAttachments (from the X-WP-Total header and local updates on add/remove).

wp.media.model.Attachments updates that total on every observed collection’s add / remove events—not only the mirrored query collection.

For featured image, the library observes:

• The query collection (uploads and server results)
• The selection collection (auto-select after upload)

After one upload:

1. Attachment is added to the query → total +1
2. autoSelect adds the same attachment to selection → total +1 again

Result: 1 item shown, total reported as 2.

Solution

Only adjust totalAttachments when the event comes from the mirrored query collection (collection === this.mirroring), not from selection, uploader queue, or other observed collections.

File changed: src/js/media/models/attachments.js

• _addToTotalAttachments
• _removeFromTotalAttachments

Demo / screen recording

Issue Reproduction Video:

current-flow.mp4

Issue Resolution Video

Issue_Resolution_Video.mp4

Use of AI Tools

AI assistance: Yes
Tool(s): Cursor (Auto)
Used for: Exploring the codebase and drafting this PR description. Final code was edited and reviewed by me.

This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request.

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