Social: render connection template in per-network preview

[manzoorwanijk]

Follow-up to #48568 (SOCIAL-453).

Proposed changes

#48568 prefilled the per-network editor's message field with connection.template when no per-post override was set, but only in the form input. This PR aligns the rest of the pipeline with that behavior:

• useRenderMessageItems: in per-network mode, fall back to connection.template (then globalMessage) when connection.message is empty, so the items POSTed to wpcom/v2/publicize/render-messages match what the form displays. Global mode is unchanged (connection.message ?? globalMessage).
• useConnectionPreviewData: apply the same fallback to baseMessage so the non-rendered fallback (templates-disabled sites, or while the rendered batch is loading) also shows the connection template.
• usePerNetworkCustomization.syncConnections: when toggling per-network mode on, do not overwrite connection.message for connections that have their own template — leaving it undefined lets the editor and preview fall back to the connection template instead of clobbering it with the global share message.

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

No.

Testing instructions

Prerequisites: site features include social-enhanced-publishing and social-message-templates, plus a Jetpack Social paid plan (so per-network customization is available).

1. Connection template flows through to the per-network preview

   • Set a connection template (e.g. Hi from {network}: {post_title}) for one connection in connection management.
   • Open the block editor for a post and open the customize-and-preview UI.
   • Enable per-network customization.
   • Open that connection's tab. The Message field should be prefilled with the connection template, and the preview pane should render that template (not the global share message).

2. Toggling per-network mode preserves the connection template

   • Set a non-empty global share message in the post's main share field.
   • Toggle per-network mode off, then on again.
   • For the connection that has its own template, the Message field should still be empty (so the connection-template prefill is shown), not the global share message.

3. Switching back to global mode does not bleed the connection template

   • After step 2, toggle per-network mode off (back to global mode).
   • The preview should render the global share message — not the connection template.

4. No regression for connections without a template

   • For a connection that does not have its own template, the per-network editor and preview should still fall back to the global share message (or default network template), as before.

5. Automated checks

   • pnpm --filter @automattic/jetpack-publicize typecheck
   • pnpm --filter @automattic/jetpack-publicize test

Before	After

[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 fix/social/per-network-connection-template branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack fix/social/per-network-connection-template

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 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 🤖

---

Follow this PR Review Process:

1. Ensure all required checks appearing at the bottom of this PR are passing.
2. Make sure to test your changes on all platforms that it applies to. You're responsible for the quality of the code you ship.
3. You can use GitHub's Reviewers functionality to request a review.
4. When it's reviewed and merged, you will be pinged in Slack to deploy the changes to WordPress.com simple once the build is done.

If you have questions about anything, reach out in #jetpack-developers for guidance!

[gmjuhasz]

Code seems straight forward and I cant reproduce the bleed with the changes

[jp-launch-control]

Code Coverage Summary

Coverage changed in 3 files.

File	Coverage	Δ%	Δ Uncovered
projects/packages/publicize/_inc/hooks/use-per-network-customization/index.ts	22/29 (75.86%)	-8.75%	3 ❤️‍🩹
projects/packages/publicize/_inc/hooks/use-connection-preview-data/index.ts	31/40 (77.50%)	-1.29%	2 ❤️‍🩹
projects/packages/publicize/_inc/hooks/use-render-message-items/index.ts	43/54 (79.63%)	2.08%	0 💚

Full summary · PHP report · JS report