JSON API: serializable_error() valid-int-only status hardening

[darssen]

Related to CONNECT-267 (problem 1)

This is a second attempt after #50047 failed deployment CI in WPCOM. More info in p1782802283094959-slack-C01U2KGS2PQ
It is less ambitious than the previous PR, but we will handle problem 2 separately.

Proposed changes

Harden WPCOM_JSON_API::serializable_error() so an error always serializes a valid HTTP status (>= 400) — never 1, a non-integer, or a 2xx an app could read as success.

The previous extraction let array-shaped error data without a status_code key fall through as a truthy array, which downstream (int)-cast to 1 (and, without http_envelope, a 200 OK) — the root of the app-crash incident. It now coerces non-numeric / array data and any < 400 value to 400.

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

No

Testing instructions

• jetpack docker phpunit jetpack -- --filter=WPCOM_JSON_API_Serializable_Error_Test — 11 tests green.
• Covers: valid status passthrough (incl. unknown-but->= 400 left unchanged), array-without-status_code -> 400 (not 1), 2xx -> 400, and the error body shape (code/message/additional_data) preserved.

[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 update/json-api-serializable-error-valid-int branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack update/json-api-serializable-error-valid-int

Interested in more tips and information?

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• 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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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.

[jp-launch-control]

Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/plugins/jetpack/class.json-api.php	66/475 (13.89%)	3.37%	-16 💚

Full summary · PHP report · JS report

[Copilot]

Pull request overview

This PR hardens WPCOM_JSON_API::serializable_error() so WP_Error responses always serialize a sane HTTP error status code (integer and >= 400), preventing array-shaped error data from being (int)-cast to 1 and avoiding accidental 2xx/3xx statuses that clients could interpret as success.

Changes:

• Coerce error status_code to an integer and default/coerce any < 400 (or non-numeric) value to 400.
• Add PHPUnit coverage for the regression cases (array-without-status_code → 400, non-error statuses → 400, unknown >= 400 statuses pass through, error shape preserved).
• Add a Jetpack plugin changelog entry for the fix.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
projects/plugins/jetpack/class.json-api.php	Hardens status extraction/coercion in serializable_error() to ensure int >= 400.
projects/plugins/jetpack/tests/php/json-api/WPCOM_JSON_API_Serializable_Error_Test.php	Adds targeted unit tests covering the regression and intended status coercion behavior.
projects/plugins/jetpack/changelog/update-json-api-serializable-error-valid-int	Adds a changelog entry describing the JSON API error-status hardening.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

[fgiannar]

LGTM