Feature Flags: re-read wpcom overrides after switch_to_blog()

[dognose24]

Proposed changes

Wpcom_Feature_Flags memoizes a site's flag overrides in a static property the first time any flag is resolved, and never re-reads them. On WordPress.com Simple, the public API process resolves flags before it switches to the requested site (premium-analytics-dashboard-composition is checked on init, for one), so the map memoized then is the process's first blog, not the site the request is for. Every override set on Tools → Feature Flags therefore applies in that site's wp-admin but not to its wpcom/v2 REST responses, which is where a Premium Analytics dashboard reads its sections from.

• Drop the memoized override map on switch_blog, so the next resolution reads the current blog's option.
• Pin it with a test that resolves a flag, changes the option behind the cache, fires switch_blog, and expects the new value. The bootstrap-wiring test now also checks the switch_blog hook.

Found while testing #52549 on a Simple site: with premium-analytics-a11n-all-sections forced on, the Feature Flags screen reported it effective, yet GET /wpcom/v2/sites/…/dashboards/…/sections kept returning the preview's two tabs. Running the same resolution in the sandbox CLI reproduced it: false after switch_to_blog(), true after reset_overrides_cache().

Related product discussion/links

• Follows Feature Flags: add an Automattician-only control screen on Simple and Atomic #51324, which added the screen.
• Unblocks Premium Analytics: let Automatticians see every section of a preview-scoped dashboard #52549 on WordPress.com Simple.

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

No.

Testing instructions

Automated:

• jp test php packages/jetpack-mu-wpcom --filter Wpcom_Feature_Flags

On a WordPress.com Simple sandbox, with a site whose Premium Analytics preview is switched on through its own opt-in and no jetpack-premium-analytics override (Traffic and Insights only), and with #52549 applied:

1. Sandbox both the site's domain and public-api.wordpress.com.
2. As an Automattician, open Tools → Feature Flags (a8c), force premium-analytics-a11n-all-sections on, and save.
3. Open https://public-api.wordpress.com/wpcom/v2/sites/<blog-id>/dashboards/jetpack-premium-analytics_dashboard/sections from the dashboard (or copy the request the tab bar makes).
4. On trunk, the response still lists only traffic and insights. With this PR, it lists every section the site qualifies for, and the dashboard's tab bar follows.
5. Set the flag back to Default. The response returns to the two preview tabs.

🤖 Generated with Claude Code

[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 fix/wpcom-feature-flags-reset-overrides-on-switch-blog branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack-mu-wpcom-plugin fix/wpcom-feature-flags-reset-overrides-on-switch-blog

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!

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Follow this PR Review Process:

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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/wpcom-feature-flags/class-wpcom-feature-flags.php	214/225 (95.11%)	0.02%	0 💚

Full summary · PHP report · JS report

[dognose24]

Superseded by #52558, which keys the cache by blog instead of resetting on switch_blog. That avoids the extra option read a switch_to_blog()/restore_current_blog() pair would trigger here, and it covers the same public-api case. Verified locally: #52558's suite passes (54 tests), and its per-blog test fails against this branch's implementation.