fix: Prevent undefined get_current_screen function errors

[dcalhoun]

Proposed changes:

Guard against invocations of an undefined get_current_screen function.

This function is undefined in certain contexts -- e.g., a REST API
request that results in enqueueing assets. Referencing an undefined
function results in a fatal error. With the get_current_screen
function specifically, it is common practice to check the function's
existence prior to invoking the it.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

N/A, no product discussion occurred for this bug fix.

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

No.

Testing instructions:

Verify feature stability with testing instructions similar to #38475.

1. Apply these changes to your testing environment.
2. Create a new page on your test site: <site_domain>/wp-admin/post-new.php?post_type=page.
3. Verify the page templates displayed match those in production and function as expected (e.g., clicking one inserts the content into the block editor).

[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 WordPress.com Simple 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, and enable the fix/prevent-undefined-get-current-screen-function-errors branch.

  • For jetpack-mu-wpcom changes, also add define( 'JETPACK_MU_WPCOM_LOAD_VIA_BETA_PLUGIN', true ); to your wp-config.php file.

• To test on Simple, run the following command on your sandbox:

  bin/jetpack-downloader test jetpack-mu-wpcom-plugin fix/prevent-undefined-get-current-screen-function-errors
  

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!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

• ✅ Include a description of your PR changes.
  
• ✅ Add a "[Status]" label (In Progress, Needs Team Review, ...).
  
• ✅ Add testing instructions.
  
• ✅ Specify whether this PR includes any changes to data or privacy.
  
• ✅ Add changelog entries to affected projects
  

This comment will be updated as you work on your PR and make changes. If you think that some of those checks are not needed for your PR, please explain why you think so. Thanks for cooperation 🤖

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The e2e test report can be found here. Please note that it can take a few minutes after the e2e tests checks are complete for the report to be available.

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Follow this PR Review Process:

1. Ensure all required checks appearing at the bottom of this PR are passing.
2. Choose a review path based on your changes:
   • A. Team Review: add the "[Status] Needs Team Review" label
     • For most changes, including minor cross-team impacts.
     • Example: Updating a team-specific component or a small change to a shared library.
   • B. Crew Review: add the "[Status] Needs Review" label
     • For significant changes to core functionality.
     • Example: Major updates to a shared library or complex features.
   • C. Both: Start with Team, then request Crew
     • For complex changes or when you need extra confidence.
     • Example: Refactor affecting multiple systems.
3. Get at least one approval before merging.

Still unsure? Reach out in #jetpack-developers for guidance!

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Mu Wpcom plugin:

• Next scheduled release: WordPress.com Simple releases happen daily.

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

[dcalhoun]

👋🏻 @miksansegundo. This is my first time modifying jetpack-mu-wpcom. Given your experience with #38475, I hoped to receive your review and help testing these changes — primarily ensuring there are no unintended regressions for the web product. Would you be willing to help?

Thank you! 🙇🏻‍♂️