Automatic upgrade path always disables image uploads — in the UI

Yay, that failing test worked! :D

Now onto fixing this…

Stepped through this with a debugger.

editor_form_filter_admin_format_editor_configure() does

    elseif (empty($editor) || $editor_value !== $editor->getEditor()) {
      $format = $form_state->getFormObject()->getEntity();
      $editor = Editor::create([
          'format' => $format->isNew() ? NULL : $format->id(),
        'editor' => $editor_value,
      ]);
      $form_state->set('editor', $editor);
    }

It's that second condition that allows entering this branch that is true when switching the text editor. While text-editor specific settings cannot be carried over, image upload settings can be, because they're embedded in the Editor config entity at the top-level, and they even have an API interface: \Drupal\editor\EditorInterface::getImageUploadSettings() + \Drupal\editor\EditorInterface::setImageUploadSettings().

Created core editor.module bug report: #3245351: Should switching text editors retain image upload settings?.

Walked @lauriii through this on a call, he says it totally makes sense 🚢