Write editor: add dismissible beta disclaimer banner

[allilevine]

Fixes RSM-2646

Proposed changes

• Add a dismissible beta disclaimer banner to the Write editor (jetpack-mu-wpcom)
• Banner displays: "Beta: This is an early-access feature. Data loss is possible."
• Once dismissed, the banner never reappears (dismissal persisted to localStorage)
• Correctly stacks with the recovery banner if both are visible simultaneously

Related product discussion/links

• RSM-2646

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

No.

Testing instructions

• Go to the Write editor (admin.php?page=write)
• The beta disclaimer banner should appear at the top of the editor
• Click × — the banner should disappear
• Refresh the page — the banner should remain hidden
• To reset: DevTools → Application → Local Storage → delete wpcom-write-disclaimer-dismissed, then refresh — the banner reappears

[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 (WordPress.com Site Helper), and enable the rsm-2646-add-disclaimer-to-editor branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack-mu-wpcom-plugin rsm-2646-add-disclaimer-to-editor

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]

Thank you for your PR!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

• ✅ Include a description of your PR changes.
  
• ✅ Add a "[Status]" label (In Progress, Needs Review, ...).
  
• ✅ Add testing instructions.
  
• ✅ Specify whether this PR includes any changes to data or privacy.
  
• ✅ Add changelog entries to affected projects
  

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/packages/jetpack-mu-wpcom/src/features/write/write.php	215/310 (69.35%)	0.20%	0 💚

Full summary · PHP report