Media & Text: Keep image size and URL in sync when selecting media - #84698

What?

Fixes #38520.

When an image is selected in the Media & Text block, the image URL, the Resolution control and the size-* class now always match.

Why?

When an image was selected, the block always used the "large" URL but never stored mediaSizeSlug. The Resolution control and the saved size-* class fall back to full, so the sidebar showed "Full Size" while the front end rendered the large image. To get the real full-size image, users had to pick another size and then switch back. A mediaSizeSlug already set on the block (for example in a pattern) was also ignored, and the site's default image size setting was not respected.

How?

In attributesFromMedia(), the size is now chosen in this order, the same way the Image and Cover blocks do it:

1. The block's current mediaSizeSlug, if the image has that size.
2. The imageDefaultSize editor setting (large by default).
3. full.

The image URL comes from that size, and the size is stored in mediaSizeSlug. Videos are unaffected. save output is unchanged, so no deprecation is needed, and the default stays large, so performance is the same.

Testing Instructions

1. Upload an image wider than the "Large" size (default 1024px), for example 2400×1600.
2. Create a post, insert a Media & Text block and select that image.
3. Check that Resolution in the block sidebar shows "Large". In the Code editor, check for "mediaSizeSlug":"large", an image src ending in -1024x… and the class size-large.
4. Save and view the post. Confirm the front end shows the same large image with size-large.
5. Change Resolution to "Full Size" and confirm the full image and the size-full class are used.
6. Replace the image with another large one and confirm "Full Size" is kept.
7. In the Code editor, paste <!-- wp:media-text {"mediaSizeSlug":"thumbnail"} --><div class="wp-block-media-text is-stacked-on-mobile"><figure class="wp-block-media-text__media"></figure><div class="wp-block-media-text__content"></div></div><!-- /wp:media-text -->, select an image, and confirm the thumbnail is used.
8. Select an image smaller than "Large" and confirm "Full Size" is shown and used.

Use of AI Tools

I used Claude Code to look into the cause and draft the change and this description. I reviewed and tested the change myself.