Here’s the repair, for good measure and anyone curious:
add_action("gform_after_submission_5", "books_promoter", 10, 4);
function books_promoter($entry, $form) {
global $post;
global $wp_query;
$post_id = get_the_ID(); // $entry['post_id'];
$post_data['status'] = get_post_meta($post_id,'status', true);
$post_data['promoter'] = get_post_meta($post_id,'promoter', true);
$status = $entry['5'];
$promoter = $entry['6'];
update_post_meta($post_id, 'books_status', $status );
update_post_meta($post_id, 'books_promoter', $promoter );
}