Editor: Warn when the featured image is also in the post

[mehmoodak]

Fixes #

Proposed changes

Many themes show the featured image at the top of a post, so it appears twice when the same image is also in the content.

• Shows a notice under the featured image when it's also in an Image block in the post or page, with a Preview link and a dismiss button.
• Adds a "Hide featured image on this post" checkbox. Ticking it hides the image on the post's own page. It still shows as the thumbnail and when the post is shared.
• The checkbox only shows where hiding is known to work: on block themes whose template has a Featured Image block, and on classic themes that declare Content Options featured image support. Other themes get the notice only.
• Unticks itself if the duplicate is removed from the content.
• New beta extension: featured-image-duplicate.

Related product discussion/links

• CM-959

Does this pull request change what data or activity we track or use?

No.

Testing instructions

1. Enable beta blocks: define( 'JETPACK_BLOCKS_VARIATION', 'beta' );
2. With a block theme (e.g. Twenty Twenty-Five), create a post, set a featured image, and insert the same image in the content.
3. Under the featured image you should see the notice and the checkbox.
4. Tick the checkbox and view the post. The image shows once. The blog home still shows the thumbnail.
5. Back in the editor, remove the image from the content. The checkbox unticks and the notice goes away.
6. Dismiss the notice, save and reload. It stays dismissed. Set a different featured image that's also in the content, and it comes back.
7. Repeat on a page. The copy says "page".
8. With a classic theme without Content Options support, you see the notice only.

No unit tests yet while this is a beta extension; covered by the manual steps above.

🤖 Generated with Claude Code

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WoA dev site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin (Jetpack), and enable the add/featured-image-duplicate-notice branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack add/featured-image-duplicate-notice

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• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

Thank you for your PR!

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Code Coverage Summary

4 files are newly checked for coverage.

File	Coverage
projects/plugins/jetpack/extensions/plugins/featured-image-duplicate/editor.js	0/4 (0.00%) 💔
projects/plugins/jetpack/extensions/plugins/featured-image-duplicate/components.tsx	17/24 (70.83%) 💚
projects/plugins/jetpack/extensions/plugins/featured-image-duplicate/featured-image-duplicate.php	78/88 (88.64%) 💚
projects/plugins/jetpack/extensions/plugins/featured-image-duplicate/index.ts	48/50 (96.00%) 💚

Full summary · PHP report · JS report

_{Coverage check overridden by Covered by non-unit tests Use to ignore the Code coverage requirement check when E2Es or other non-unit tests cover the code .}