Interface previews/skeleton screens through optional "preview" or "placeholder" templates

Fixed failed commands on #88
Attached patch against Drupal 10.1.x
Attached interdiff

Awesome work, love the additional test coverage as well.

Can confirm it works,
1. i've added the recent content block to the sidebar
2. created: core/themes/olivero/templates/block/big-pipe-interface-preview--block--views-block--content-recent-block-1.html.twig with some barebones placeholders for the recent content block
3. added a sleep to make sure we can see the preview

et voila;

Haven't looked at the MR in detail yet but we need a change record for this since it's a new API.

Added change record

Reviewed the code & tests in detail. I think we could potentially still add some more test coverage for the simplified suggestions, but I didn't think that was a hard requirement for this to be committed.

Committed aeac296 and pushed to 10.1.x. Thanks!

Tagging for 10.1.0 release highlights since this is a pretty big developer facing feature.

lauriii → closed merge request !3312

Superb! 🤩 Thank you for making happen what I hoped to do many years ago and never got around to finishing! 🙏

The first use of this new infrastructure just landed in 🐛 Improve rendering account link in the toolbar Fixed ! 🥳

Also, thanks to this issue, I was able to close 🐛 Lazy builder placeholders should show a loading indicator Closed: outdated 👍

Automatically closed - issue fixed for 2 weeks with no activity.