Handler receives the envelope instead of the message it was registered for #341

Worker::process() passes the message into the consume pipeline exactly as it arrived, and ConsumeFinalHandler hands that to the handler. Nothing unwraps an envelope on the way, so a handler written the way the guide writes it breaks as soon as the message is wrapped.

The documented handler (docs/guide/en/messages-and-handlers.md:108):

public function handle(MessageInterface $message): void
{
    assert($message instanceof SendEmailMessage);
    $this->mailer->send($message->to, $message->subject, $message->body);
}

Called with an adapter-assigned id, which is the normal asynchronous path:

$worker->process(new IdEnvelope($message, 'id-42'), 'test');

With zend.assertions=1:

MessageFailureException: Processing of message #id-42 is stopped because of an exception:
assert($message instanceof SendEmailMessage).

With zend.assertions=-1, the production default:

Warning: Undefined property: Yiisoft\Queue\Message\IdEnvelope::$to
sending to: NULL

No error, and the work is done against empty values. DelayEnvelope and FailureEnvelope behave the same way. Call path: Worker.php:45 → ConsumeMiddlewareDispatcher → ConsumeFinalHandler.php:21.

Worth deciding which contract is meant:

• unwrap in Worker before dispatching, so a handler always receives the message type it was registered for, and offer the envelope separately to handlers that want the metadata, or
• keep passing the envelope and change every handler example in the guide to unwrap first ($message instanceof Envelope ? $message->getMessage() : $message), since assert() is not a guard in production.

InMemoryAdapter happens not to trigger this because it stores the unwrapped message, but any adapter that stores what push() returned does.

#338 reworks Worker and the pipeline around it, so this probably wants deciding before that lands.