php-qml/framework/php/src/CorrelationContext.php

<?php

declare(strict_types=1);

namespace PhpQml\Bridge;

/**
 * Default implementation of {@see CorrelationContextInterface}: a plain
 * per-request holder for the `Idempotency-Key` value.
 *
 * Stashed here on RequestEvent (see {@see EventSubscriber\CorrelationKeyListener})
 * and read back by {@see ModelPublisher} when it builds Mercure envelopes,
 * so QML clients can match Mercure echoes to the optimistic mutation that
 * originated them (PLAN.md §4 *Idempotency*, §5 *Optimistic updates*).
 *
 * Cleared on TerminateEvent. CLI commands and out-of-request mutations
 * see no correlation key, which is the correct behaviour.
 */
final class CorrelationContext implements CorrelationContextInterface
{
    private ?string $key = null;

    public function set(?string $key): void
    {
        $this->key = $key;
    }

    public function get(): ?string
    {
        return $this->key;
    }

    public function clear(): void
    {
        $this->key = null;
    }
}