== RabbitMQ: there is nothing to replay ==

first drain of the queue  : 12 messages
second drain of the queue : 0 messages
queue depth afterwards    : 0

Acknowledging a message deletes it. The broker is a router with buffers,
not a log: there is no offset to rewind and no second reader that can see
what the first one consumed. Reading the same message twice means
arranging it in advance -- a second queue bound to the same exchange, or a
copy written somewhere else -- and it cannot be arranged after the fact.