SEO: remove the rsm_jetpack_seo feature flag (JETPACK-1702)

[angelablake]

Proposed changes

Retire the rsm_jetpack_seo launch flag now that the Jetpack SEO product is built and merged. With the flag gone, the SEO surface is governed solely by the install-cohort visibility rules that already shipped in PR #5c (#49672) / #5b (#49697):

• Initializer::init() no longer bails on the feature flag. The discoverability cohort gate (is_seo_surface_visible()) is now the only gate: fresh installs and all WordPress.com sites (Simple + Atomic) are visible; existing self-hosted installs stay hidden until they opt in (legacy Traffic page / My Jetpack).
• Initializer::is_optin_available() simplifies to ! is_seo_surface_visible() — the opt-in surfaces (Traffic-page banner, My Jetpack card) now show purely on cohort state.
• Legacy Traffic plugin-search hint (modules/plugin-search.php) now keys off the SEO dashboard's per-site availability (Initializer::is_seo_surface_visible(), guarded by class_exists) instead of the global flag, so its CTAs never point to a page that isn't registered on that site.
• Drop the now-unused FEATURE_FILTER constant and the flag-driven unit tests; refresh the My Jetpack opt-in-card docblock that described the flag.

No data-shape changes: seo.optin_available and seo.surface_visible are still injected (now unconditionally rather than flag-gated), so the legacy Traffic page reads them exactly as before.

Why

rsm_jetpack_seo was added at the foundation merge to hide the in-progress product. The product is complete and the cohort rollout is in place, so removing the flag is the final pre-launch step (JETPACK-1702). After this lands, the SEO dashboard becomes available per the cohort rules on the next release.

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

No new tracking. The Tracks work is handled separately (JETPACK-1728).

Testing instructions

On a build of this branch:

• Self-hosted, fresh install: SEO menu appears in wp-admin automatically; the legacy Traffic SEO/Sitemaps/Verification sections are replaced by the "SEO has its own dashboard" pointer.
• Self-hosted, existing install (not opted in): no SEO menu; the legacy Traffic SEO sections + the opt-in banner are present; opting in (banner or My Jetpack card) reveals the menu.
• WordPress.com (Simple / Atomic): SEO menu appears with nothing to wire (the cohort check short-circuits to visible). This is the case to confirm on the wpcom sandbox.
• Search the wp-admin plugin directory for "seo"/"sitemap": the SEO Tools hint appears only where the dashboard is registered (visible cohort), and its CTAs open admin.php?page=jetpack-seo.

Test environments

• Simple
• Atomic
• Self-hosted (fresh)
• Self-hosted (existing / opt-in)

Screenshots

Screenshots to be added by author.

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⚠️ This is the launch flip. Holding merge until: (1) the WordPress.com/Simple menu is confirmed on the sandbox, and (2) removal timing is coordinated with @dhasilva (who added the flag), per JETPACK-1702.

[github-actions]

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

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Follow this PR Review Process:

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Jetpack plugin:

The Jetpack plugin has different release cadences depending on the platform:

• WordPress.com Simple releases happen as soon as you deploy your changes after merging this PR (PCYsg-Jjm-p2).
• WoA releases happen weekly.
• Releases to self-hosted sites happen monthly:
  • Scheduled release: July 7, 2026
  • Code freeze: July 6, 2026

If you have any questions about the release process, please ask in the #jetpack-releases channel on Slack.

[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 remove/rsm-jetpack-seo-flag branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack remove/rsm-jetpack-seo-flag

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

[jp-launch-control]

Code Coverage Summary

Coverage changed in 2 files.

File	Coverage	Δ%	Δ Uncovered
projects/plugins/jetpack/modules/plugin-search.php	0/269 (0.00%)	0.00%	1 ❤️‍🩹
projects/packages/seo/src/class-initializer.php	142/221 (64.25%)	0.13%	-1 💚

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