<?php
define('WP_USE_THEMES', true);

require __DIR__ . '/wp-load.php';
wp();

ob_start();
require ABSPATH . WPINC . '/template-loader.php';
$html = ob_get_clean();

file_put_contents(
    __DIR__ . '/probe3.txt',
    "HTML_SIZE=" . strlen($html) . "\n" .
    "OB_LEVEL=" . ob_get_level() . "\n" .
    "HEADERS=" . print_r(headers_list(), true)
);

header_remove('Content-Length');
echo $html;