Disable Block UI for regions managed by Experience Builder

We should clearly indicate in this UI, if a region is managed by Experience Builder.

"A" region? It's either all or no regions.

It's been like that since the very start: 📌 Introduce an XB `PageTemplate` config entity Active .

IMHO the correct solution is to override the block.admin_display and block.admin_display_theme routes and make it do:

class XbBlockListController extends BlockListController {
  public function listing($theme = NULL, ?Request $request = NULL) {
    $build = parent::listing($theme, $request);
    assert(is_array($build));

    $template = match ($theme) {
      NULL => PageTemplate::forActiveTheme();
      default => PageTemplate::load($theme);
     };
    $xb_page_template_for_theme = $template && $template->status();
    if ($xb_page_template_for_theme) {
      $build['warning'] = ['#weight' => - 10000, '#markup' => 'This UI currently has no effect BLABLABLA.'];
    }

    return $build;
  }
}

Maybe I don't understand what this setting is doing 🤔 What happens to the regions that are not exposed to Experience Builder? I thought they would be managed by Block Layout but turns out that probably isn't the case.

What happens to the regions that are not exposed to Experience Builder?

They would just remain empty, i.e. unused.

I think we need to update the UI to clarify this because this is not at all what I expected 😅 I think #5 makes sense as a direction for this based on what this UI actually does.

Attaching updated preview of the Block UI page.

#8: I'm very surprised that #7 is not what you expected, because:
you definitely know better than most how the Block functionality works.
the checkbox literally says , not

Is it the bit in the description perhaps? I think modifying that to

MR reviewed! This is on the right track, but there's a bunch of rough edges.

Almost there!

This is what the current MR does:

I personally don't think this message is sufficiently clear. It doesn't implement my suggestion from #11 yet. But I'll let @lauriii be the judge.

Updated title to reflect A) current XB reality, B) current proposed solution.

I have updated the warning message and added the suggestion by @wim leers in #11.
If it still doesn't suit then maybe @laurii can provide the message that is to be displayed.
Thank you!