wp-block-group__inner-container markup is missing on new default Group blocks

[jeremyfelt]

Description

In #42763 and #44176, the "constrained" layout was set as the default for the Group block and the default variation used when inserting a Group block into content was updated.

I believe the reasoning for this was to preserve existing "default" Group blocks—these have an inner container injected on the front-end in classic themes for backward compatibility—while also changing some other defaults about the Group block itself. (It's late and I didn't really parse everything, but #42763 is a very nicely documented PR!). 😄

This change doesn't immediately break backward compatibility in that existing groups remain as is and have the same markup on the front-end.

However, any new Group blocks inserted into content on an existing site have different markup and may now appear broken on the front-end, even though a person maintaining their site has used the same process for years.

If <!-- wp:group {"layout":{"type":"constrained"}} --> is the new "default" Group block, then it makes sense from a user experience perspective (IMO) to include it as one of those in which an inner container is injected in classic themes.

Step-by-step reproduction instructions

1. On WordPress 6.0.2, add a new page, add a group block, view the markup: see an inner container.
2. With Gutenberg 14.2 added, do the same: see no inner container.

Screenshots, screen recording, code snippet

No response

Environment info

• WordPress 6.0.2
• Gutenberg 14.2

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes

[Mamaduka]

cc @tellthemachines, @youknowriad