WordPress MU plugin: auto-reloads when CSS/JS files 403 due to Apache inode cache lag

403-reload-workaround.php

<?php
/**
 * Plugin Name: 403 Reload Workaround
 * Description: Auto-reloads when CSS/JS files 403 due to Apache inode cache lag.
 * Plugin URI: https://gist.github.com/chrisdavidmiles/aeb6b4cfe4246c3c95c45f9a40d9c74b
 * Version: 0.1
 * Author: Chris Miles
 */

add_action('init', function() {
    if (!is_admin() || !current_user_can('manage_options')) return;
    if (!isset($_GET['reload_403_toggle'])) return;

    check_admin_referer('reload_403_toggle');
    $new = ($_GET['reload_403_toggle'] === 'disable') ? 'disabled' : 'enabled';
    update_option('reload_403_status', $new);
    wp_safe_redirect(remove_query_arg(['reload_403_toggle', '_wpnonce']));
    exit;
});

add_filter('plugin_action_links_' . plugin_basename(__FILE__), function($links) {
    $disabled = get_option('reload_403_status') === 'disabled';
    if ($disabled) {
        $url = wp_nonce_url(add_query_arg('reload_403_toggle', 'enable'), 'reload_403_toggle');
        $links[] = '<a href="' . esc_url($url) . '">Enable</a>';
    } else {
        $url = wp_nonce_url(add_query_arg('reload_403_toggle', 'disable'), 'reload_403_toggle');
        $links[] = '<a href="' . esc_url($url) . '">Disable</a>';
    }
    return $links;
});

if (get_option('reload_403_status') === 'disabled') return;

add_action('wp_head', 'reload_403_inline_script', 1);
add_action('admin_head', 'reload_403_inline_script', 1);

function reload_403_inline_script() {
    ?>
    <script>
    (function() {
        var key = '_403rr_' + location.pathname;
        var state = parseInt(sessionStorage.getItem(key) || '0', 10);
        var tsKey = key + '_t';
        var ts = parseInt(sessionStorage.getItem(tsKey) || '0', 10);

        if (ts && Date.now() - ts > 30000) {
            state = 0;
            sessionStorage.removeItem(key);
            sessionStorage.removeItem(tsKey);
        }

        if (state === 1) {
            sessionStorage.setItem(key, '2');
            setTimeout(function() { location.reload(); }, 2000);
            return;
        }

        if (state >= 2) {
            sessionStorage.removeItem(key);
            sessionStorage.removeItem(tsKey);
            return;
        }

        function check() {
            var entries = performance.getEntriesByType('resource');
            for (var i = 0; i < entries.length; i++) {
                var e = entries[i];
                if (e.responseStatus === 403 && /\.(css|js)(\?|$)/i.test(e.name)) {
                    sessionStorage.setItem(key, '1');
                    sessionStorage.setItem(tsKey, String(Date.now()));
                    location.reload();
                    return;
                }
            }
        }

        if (document.readyState === 'complete') {
            check();
        } else {
            window.addEventListener('load', check);
        }
    })();
    </script>
    <?php
}