How to validate required fields of File attached to current edited item?

I’m looking for a way to validate not only the current edited item (ie. Page, or Article) but also fields of its related files. What I mean: each related file can have its meta fields, like alt attrib - or, like here I have - the “image_license” droplist, which is set to required: true

title: Project Image

accept:
  mime: image/jpeg, image/png
sections:
  content:
    type: fields
    fields:
      image_license:
        label:
          en: Image license
          de: Bild Lizenz
        type: select
        required: true

The thing is, that Kirby allows to create an article, to upload a file, and then when saving - it doesn’t validate that file’s fields - so it actually allows to save the article not fully validated. It only validates the direct fields of the article, but the file’s fields are only validated when I open the file details - but I need that to block saving the article, if its sub-items like file attachment is also not fully filled up - these must be filled too.

On the screenshots below example - the “Image license” field is marked as required, but checked only in this view. It could be also checked / expected to be filled up directly on that image upload screen, where it checks file type - but I also couldn’t find a way to do that.

How that can be achieved? Possibly without modifying Kirby source code, but with plugins or configuration

Did I describe that clearly? It’s a simple thing, but maybe not that obvious to explain.

You could solve this via a hook that prevents publishing a page if this information is missing: page.changeStatus:before | Kirby CMS

Additionally, maybe add an info field somewhere in the page that displays missing meta information per file together with a link to the file.