Add a way to make media captions not editable in CKEditor

Fixed custom command failed. Attached interdiff for the same.

Thanks @prudloff for reporting and @Gauravmahlawat for the patch. Updating the category because adding a new feature is a feature request rather than a bug :)

Tested the feature request with the steps mentioned in Issue summary.
Applied the Patch provided #3
Tested on v9.4.x-dev
- Patch successfully applied
- Checkbox provided to enable disable the the Caption

The JS still needs some work, the entire caption field freezes

Code Review.
editor.config.DrupalMediaLibrary_enableCaptioning Not defined.
This needs to be set and passed in getConfig

/**
   * {@inheritdoc}
   */
  public function getConfig(Editor $editor) {
    if ($editor->hasAssociatedFilterFormat()) {
      $filters = $editor->getFilterFormat()->filters();
      if ($filters->has('media_embed')) {
        $filter_caption = $filters->get('media_embed')->settings->enable_captioning;
      }
    }
    return [
      'drupalMedia_previewCsrfToken' => \Drupal::csrfToken()->get('X-Drupal-MediaPreview-CSRF-Token'),
      'DrupalMediaLibrary_enableCaptioning' => $filter_caption ?? 0,
    ];
  }

media schema needs to be updated

    enable_captioning:
      type: boolean
      label: 'Enable captioning'

Create a issue fork, Applied the patch and updated the code
- This will enable/disable the caption checkbox entirely form the form.
https://git.drupalcode.org/project/drupal/-/merge_requests/1893/diffs#c9...
- Passed the variable value for DrupalMediaLibrary_enableCaptioning
https://git.drupalcode.org/project/drupal/-/merge_requests/1893/diffs#86...
- Updated the schema

Pending/Todo
The Js code still needs some review/fix

Another way to do this is to just change the editable caption selector to include a check for a data attribute on the figcapture tag. E.g.:

        editables: {
          caption: {
            selector: 'figcaption:not([data-no-edit])',
            allowedContent: 'a[!href]; em strong cite code br',
            pathName: Drupal.t('Caption')
          }
        },

This :not([data-no-edit']) part means that if the twig template uses:

<figcaption data-no-edit="1" .... >

The caption will not be editable.

With a little research, I found a way to modify the editable caption selector without patching core.

Basically, you need a custom bit of JS to run when CKEDITOR is initialized. This can be in your theme (the one used for editing) or added via a custom module. Here's the basic JS to run:

Drupal.behaviors.customCKEditorConfig = {
  attach: function (context, settings) {
    if (typeof CKEDITOR !== "undefined") {
      // When each CKEDITOR instance is created on the form page.
      CKEDITOR.on('instanceCreated', function (e) {
        var instance = e.editor;
        // Run code when the instance is initialized.
        instance.on('instanceReady', function (e) {
          var instance = e.editor;
          // Change caption selector
          if ('drupalmedia' in instance.widgets.registered) {
            instance.widgets.registered.drupalmedia.editables.caption.selector = 'figcaption:not([data-no-edit])';
          }
        });
      });
    } 
  }
}

Update your template with figcapture to include the data-no-edit attribute to prevent caption editing.

With CKEditor 5, included in Drupal 10 core, it looks like media caption is already not editable. CKE4 is unsupported and needs a contrib module.