Searching with "Next Post ID" is giving me the Previous/Next Post Navigation, but my question is not related to that.

In WordPress Admin panel, when we're attempting to create a new post the post is been automatically saved as 'auto-draft' and the post ID is been placed within the form as a hidden field named post_id. So when the post is submitted and the $_REQUEST['post_id'] is been isset.

I'm trying to move uploaded attachments with a Custom Post Type to it's designated directory under uploads/ like uploads/my-dir/my-item-{post_id}. I'm following Rian Rietveld's snippet for the move. And attachments from admin panel is moving perfectly:

/**
 * Set the attachment Upload path.
 *
 * Set a custom upload path for the post attachments for
 * easy management.
 *
 * @param array $upload Default directory.
 *
 * @author Rian Rietveld
 * @link   
 *
 * @return array Defined directory for the App.
 */
public function my_attachment_dir( $upload ) {
    if ( ! empty( $_REQUEST['post_id'] ) ) {
        $id = $_REQUEST['post_id'];

        // Check whether the posttype is ours.
        if ( 'my-cpt' === get_post_type( $id ) ) {
            $cpt_directory = "my-item-{$id}";
            $upload['subdir'] = "/my-dir/{$cpt_directory}";
        }

        $upload['path'] = $upload['basedir'] . $upload['subdir'];
        $upload['url']  = $upload['baseurl'] . $upload['subdir'];
    }

    return $upload;
}

add_filter( 'upload_dir', 'my_attachment_dir' );

But the issue is, I can't pass a hidden field with post ID from the front end, so the $_REQUEST['post_id'] is getting unset, and the filter is not working. The attachments are uploading to its typical year-month directory.

The question I have, could be answered by any of the following:

1. How can I get the upcoming post ID in front end? or,
2. How to add filter to upload_dir with a makeshift $post_id instead of passing through $_REQUEST?