Tell harness modular host

<?php
require 'examples/boot.php';
require_once dirname(__DIR__).'/Support.php';

use Cognesy\Agents\Drivers\Testing\FakeAgentDriver;
use Cognesy\Tell\Composition\TellModuleDefinition;
use Cognesy\Tell\Contracts\CanObserveTellExecution;
use Cognesy\Tell\Contracts\Data\TellEventEnvelope;
use Cognesy\Tell\Runtime\TellPaths;
use Cognesy\Tell\Composition\TellHost;
use Cognesy\Tell\TellRequest;

$project = TellHarnessExample::project();
$events = new ArrayObject;
$observer = new class($events) implements CanObserveTellExecution {
    public function __construct(private ArrayObject $events) {}

    public function observe(TellEventEnvelope $event): void
    {
        $this->events->append($event->toArray());
    }
};
$observation = new TellModuleDefinition(
    id: 'observation.example',
    provides: [CanObserveTellExecution::class],
    factory: static fn (): object => $observer,
);
$paths = new TellPaths(
    packageAgents: dirname(__DIR__, 3).'/packages/tell/resources/agents',
    home: $project.'/.tell-host-example',
);
$host = TellHost::standard(
    directory: $project,
    paths: $paths,
    driverFactory: static fn () => FakeAgentDriver::fromResponses('host-controlled answer'),
)->replace('observation.standard', $observation)->boot();

try {
    $result = $host->runner()->run(TellRequest::prompt('Run through the host.')->withDirectory($project));
    $description = $host->describe();

    echo trim($result->text())."\n";
    echo 'Modules: '.count($description->modules)."\n";
    echo 'Observed events: '.count($events)."\n";

    assert(trim($result->text()) === 'host-controlled answer');
    assert(count($events) > 0);
} finally {
    $host->dispose();
    TellHarnessExample::remove($project);
}