Have following worker:

$handler = static function (){
    xdebug_connect_to_client();
    print "hello world";
};

// to prevent memory leaks we finish worker every 10 000 requests
$maxRequests = (int)($_SERVER['MAX_REQUESTS'] ?? 5);
for($processedRequests = 0; $processedRequests < $maxRequests; $processedRequests++) {

    // keep running will be false if server (Caddy) is terminating to allow our code to finish
    $keepRunning = \frankenphp_handle_request($handler);
    if (!$keepRunning) break;
}

Following dockerfile:

FROM dunglas/frankenphp:1.6-php8.3-bookworm

RUN install-php-extensions xdebug-^3.3

EXPOSE 80