@valendesigns I think this isn't right. The saved event is triggered on the api inside the controls itself. Why send this customized-posts-purge-trash message from the preview?

Why not just do in customize-posts.js:

api.bind( 'saved', function() {
    component.purgeTrash();
} );

is_singular() always returned false when called from the pane. So I needed access to that value to force the preview to reload the archive.

I think it would be better to keep track of whatever the last data sent from customized-posts was instead.

component.previewedQuery = new api.Value( {} );
api.previewer.bind( 'customized-posts', function ( data ) {
    var query = {};
    _.each( [ 'isSingular', 'isPostPreview', 'queriedPostId' ] ).each( function( key ) {
        query[ key ] = data[ key ];
    } );
    component.previewedQuery.set( query );
} );

Then at any time you can access whether the preview isSingular via query.previewedQuery.get().isSingular.

This would be a basic implementation of https://core.trac.wordpress.org/ticket/36582

This needs to be:

$result = wp_trash_post( $this->post_id );

I think this is wrong. We should instead be doing this change below:

if ( 'trash' !== $post_data['post_status'] && apply_filters( 'wp_insert_post_empty_content', $maybe_empty, $post_data ) ) {