Domain

1.php

<?php
final class Proposal
{
    /** @var Freelancer */
    private $freelancer;

    /** @var Money */
    private $hourRate;

    /** @var string */
    private $coverLetterMessage;

    public function __construct(Freelancer $freelancer, Money $hourRate, string $coverLetterMessage)
    {
        $this->freelancer = $freelancer;
        $this->hourRate = $hourRate;
        $this->coverLetterMessage = $coverLetterMessage;
    }
}

final class Freelancer
{
    /** @var Email */
    private $email;

    /** @var Money */
    private $hourRate;

    public function __construct(Email $email, Money $hourRate)
    {
        $this->email = $email;
        $this->hourRate = $hourRate;
    }

    public function makeProposal(string $coverLetterMessage): Proposal
    {
        return new Proposal($this, $this->hourRate, $coverLetterMessage);
    }
}

final class Job
{
    /** @var Customer */
    private $customer;

    /** @var JobDescription */
    private $description;

    /** @var Proposal[] */
    private $proposals;

    /** @var int */
    private $proposalsLimit;

    private function __construct(Customer $customer, JobDescription $description)
    {
        $this->customer = $customer;
        $this->description = $description;
        $this->proposals = [];
        $this->proposalsLimit = 0;
    }

    public static function post(Customer $customer, JobDescription $description): Job
    {
        return new Job($customer, $description);
    }

    public function newProposal(Freelancer $freelancer, string $coverLetterMessage)
    {
        $this->proposals[] = $freelancer->makeProposal($coverLetterMessage);
    }
}

2.php

<?php
final class Proposal
{
    /** @var Freelancer */
    private $freelancer;

    /** @var Money */
    private $hourRate;

    /** @var string */
    private $coverLetterMessage;

    public function __construct(Freelancer $freelancer, Money $hourRate, string $coverLetterMessage)
    {
        $this->freelancer = $freelancer;
        $this->hourRate = $hourRate;
        $this->coverLetterMessage = $coverLetterMessage;
    }
}

final class Freelancer
{
    /** @var Email */
    private $email;

    /** @var Money */
    private $hourRate;

    public function __construct(Email $email, Money $hourRate)
    {
        $this->email = $email;
        $this->hourRate = $hourRate;
    }

    public function apply(Job $job, string $coverLetterMessage)
    {
        $job->newProposal(new Proposal($this, $this->hourRate, $coverLetterMessage));
    }
}

final class Job
{
    /** @var Customer */
    private $customer;

    /** @var JobDescription */
    private $description;

    /** @var Proposal[] */
    private $proposals;

    /** @var int */
    private $proposalsLimit;

    private function __construct(Customer $customer, JobDescription $description)
    {
        $this->customer = $customer;
        $this->description = $description;
        $this->proposals = [];
        $this->proposalsLimit = 0;
    }

    public static function post(Customer $customer, JobDescription $description): Job
    {
        return new Job($customer, $description);
    }

    public function addProposal(Proposal $proposal)
    {
        $this->proposals[] = $proposal;
    }
}