Newsletter: Drop dead admin-ui build-style import; pin admin-ui 2.1.0

[CGastrell]

Proposed changes

Consumer-side adaptation for @wordpress/admin-ui 2.x in the Newsletter package. The dashboard SCSS currently @includes a stylesheet that no longer exists in admin-ui 2.x:

@include meta.load-css("@wordpress/admin-ui/build-style/style.css");

admin-ui 2.x ships its CSS via runtime DOM injection from the JS module — the build-style/ directory was removed from the package's exports. Once @wordpress/admin-ui is bumped, the SCSS pipeline 404s on that import and the dashboard build fails.

Two changes:

• Drop the dead meta.load-css line in projects/packages/newsletter/routes/dashboard/route.scss and leave a brief comment explaining why. The @wordpress/dataviews/build-style/style.css import next to it stays — dataviews still ships that file and the import is correct.
• Bump @wordpress/admin-ui in projects/packages/newsletter/package.json from 1.12.0 to 2.1.0. The package's <AdminPage> use is through @automattic/jetpack-components, which already targets admin-ui 2.x — this is just the consumer-side declaration.

This mirrors the precedent fix landed for packages/scan in commit 626cb33ea84 (#48410). This is not the monorepo-wide bump — that's #48404's job.

Related product discussion/links

• Precedent: Update Admin UI package and adapt to use visual prop for Jetpack logo #48410 (commit 626cb33ea84, merged 2026-05-07)
• Driving Renovate PR: Update Bundled @wordpress/* monorepo #48404

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

No.

Testing instructions

• Pull this branch and run pnpm install.
• Run pnpm jetpack build packages/newsletter. Build completes successfully (SCSS @include no longer 404s).
• Confirm the produced build/newsletter.css is non-empty and contains the dataviews styles (they're still loaded via meta.load-css).
• Smoke test the Newsletter dashboard in the browser (/wp-admin/admin.php?page=jetpack-newsletter-dashboard) and verify the Subscribers list and inspector panel still render with the expected admin-ui-driven layout. admin-ui 2.x injects its base styles at runtime — no static stylesheet to load.

[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 or WordPress.com Site Helper), and enable the fix/newsletter-admin-ui-scss-import branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack fix/newsletter-admin-ui-scss-import

bin/jetpack-downloader test jetpack-mu-wpcom-plugin fix/newsletter-admin-ui-scss-import

Interested in more tips and information?

• 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]

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Code Coverage Summary

This PR did not change code coverage!

That could be good or bad, depending on the situation. Everything covered before, and still is? Great! Nothing was covered before? Not so great. 🤷

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