A4A: Dismiss checkout errors after leaving checkout

[cleacos]

Resolves A4A-3163

Proposed Changes

• Add an A4A-owned cart-message cleanup lifecycle inside Billing Dragon checkout.
• Remove regular and persistent checkout error notices when A4A checkout unmounts.
• Clear cached cart messages on exit so old endpoint errors cannot replay.

Why are these changes being made?

WPCOM cart validation errors currently use persistent global notices. They can remain visible outside A4A checkout and replay from cached cart state after the user fixes the problem.

Testing Instructions

• Use an agency with an existing yearly Pressable plan.
• Select a monthly Pressable upgrade, add it to the cart, and open checkout.
• Verify that the cart validation error appears.
• Go back and change the selected upgrade to a yearly Pressable plan.
• Open checkout again.
• Verify that the previous notice was dismissed after leaving checkout, does not appear again, and checkout loads normally.

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• For UI changes, have you tested the affected components in dark mode?
• Have you tested accessibility for your changes? Ensure the feature remains usable with various user agents (e.g., browsers), interfaces (e.g., keyboard navigation), and assistive technologies (e.g., screen readers) (PCYsg-S3g-p2).
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the “[Status] String Freeze” label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
  • For UI changes, have you tested the change in various languages (for example, ES, PT, FR, or DE)? The length of text and words vary significantly between languages.
• For changes affecting Jetpack: Have we added the “[Status] Needs Privacy Updates” label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?

— ClemenAgent (Powered by Codex)

[github-actions]

WordPress.com

• Dashboard Live (direct link)

  https://calypso.live?image=registry.a8c.com/calypso/app:build-192238&env=dashboard

• Calypso Live (/home) (direct link)

  https://calypso.live/home?image=registry.a8c.com/calypso/app:build-192238

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Automattic for Agencies

• Dashboard Live (direct link)

  https://calypso.live?image=registry.a8c.com/calypso/app:build-192238&env=dashboard-a4a

• Automattic for Agencies Live (direct link)

  https://calypso.live?image=registry.a8c.com/calypso/app:build-192238&env=a8c-for-agencies

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Jetpack Cloud Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-192238&env=jetpack

[vitozev]

It works as expected. I wonder whether this could be an issue we may have on the WP.com checkout too, and if that's the case, it's probably worth fixing the issue there. But let's ship this and reach out to Shillings for feedback.