Plugin Conflicts Guardian: default pcg_guard_updates to true

[arthur791004]

Proposed changes

Follow-up to #48553 (which flipped pcg_guard_activation to default true). This flips the second gate, pcg_guard_updates, the same way:

• update-healthcheck.php — both apply_filters( 'pcg_guard_updates', false ) callsites (snapshot capture on upgrader_pre_install, post-update healthcheck on upgrader_process_complete) now default true.
• probe-endpoint.php — drops the per-mode default split ($gate_default = ! $is_update_mode) introduced when only activation defaulted on. With both gates now default true the probe endpoint applies true uniformly: apply_filters( $gate_filter, true ).
• README.md — updates the pcg_guard_updates line to "Defaults true."

No behavior change for sites that have explicitly filtered pcg_guard_updates to false. For everyone else: post-update probes run, and a fatal-on-update triggers the snapshot-based rollback flow that PCG already had wired up but defaulted dark.

Related product discussion/links

• Prior switch: Plugin Conflicts Guardian: default pcg_guard_activation to true #48553 (defaulted pcg_guard_activation to true).

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

Indirectly — pcg_guard_updates controls whether the Update rolled back logstash event from #48565 fires in the wild. The event payload itself is unchanged.

Testing instructions

1. Sync jetpack-mu-wpcom to a test site (no explicit pcg_guard_updates filter set).
2. Install a "good" plugin and activate it.
3. Update it to a version that fatals only at runtime (passes the parse-error gate).
4. Expected: post-update probe fails, plugin rolls back to its snapshot, admin notice points at the failed update, and one Update rolled back row lands in the plugin-conflicts-guardian logstash bucket.
5. Add add_filter( 'pcg_guard_updates', '__return_false' ); and repeat — expected: snapshot is not captured, no probe runs, update completes (or fatals) without rollback.
6. Activation guard regression check: clicking Activate on a fataling plugin still blocks via the activation guard (unchanged).

🤖 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 try/pcg-guard-updates-default-true branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack-mu-wpcom-plugin try/pcg-guard-updates-default-true

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]

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Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/probe-endpoint.php	0/81 (0.00%)	0.00%	-1 💚

Full summary · PHP report