Boost: Add upgrade notices and a manual Critical CSS Generate step

[LiamSarsfield]

Fixes BOOST-749

Proposed changes

Modern Settings shows Critical CSS, Image CDN, and Cornerstone upsells as info notices without monthly prices. Enabling free manual Critical CSS now waits for Generate, adding a deliberate step; legacy auto-start and paid automatic CSS stay unchanged. After invalidation, a free modern site serves no Critical CSS until Generate is pressed. A status well shows progress and results, with partial failures in a warning notice.

Related product discussion/links

Desktop comparison · Mobile comparison · Design comparison · RTL

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

No. Existing upgrade tracking and the Boost interstitial destination are unchanged.

Testing instructions

• Enable rsm_jetpack_ui_modernization_boost on a free site. Enable manual Critical CSS, then click Generate. Check idle, progress, completed, and partial-failure states; follow the recommendations link.
• Check all three upsells at desktop/mobile widths and RTL. Offline sites must hide them.
• Disable the filter and check the legacy dashboard.

Verified locally with SCRIPT_DEBUG=false: manual states, 447 Jest tests, typecheck, ESLint, and Stylelint. Legacy code paths and shared translation strings are unchanged. Rendered legacy Settings HTML is identical; screenshots at 1280 and 782 are pixel-identical.

Follow-up

The well’s info icon is deliberately omitted until tooltip copy is supplied.

Reuse check

Reuse @wordpress/ui Notice, Button, Stack, and Text, plus the existing progress bar and generation action. No shared well exists; its tokens follow the cache-log surface.

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 19 files. Only the first 5 are listed here.

File	Coverage	Δ%	Δ Uncovered
projects/plugins/boost/app/assets/src/js/features/critical-css/critical-css-meta/critical-css-meta.tsx	15/15 (100.00%)	0.00%	0 💚
projects/plugins/boost/app/assets/src/js/features/critical-css/critical-css-module/critical-css-module.tsx	8/8 (100.00%)	0.00%	0 💚
projects/plugins/boost/app/assets/src/js/features/upgrade-cta/upgrade-cta.tsx	13/14 (92.86%)	1.95%	0 💚
projects/plugins/boost/app/assets/src/js/features/critical-css/critical-css-context/critical-css-context-provider.tsx	45/59 (76.27%)	1.69%	-1 💚
projects/plugins/boost/app/assets/src/js/features/critical-css/error-description/error-description.tsx	1/14 (7.14%)	7.14%	-1 💚

1 file is newly checked for coverage.

File	Coverage
projects/plugins/boost/app/assets/src/js/features/critical-css/critical-css-meta/modern-critical-css-status.tsx	12/12 (100.00%) 💚

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