parked verifiedimportant

When a destination cannot take more mail, the engine parks the surplus in a temporary queue named after it rather than holding it in memory. The count is therefore a direct measure of how much a throttle is holding — the number a warm-up interface actually wants, and the only per-destination backlog MailerQ exposes. It is also the counter that explains a node whose broker queue is empty and which is still not sending: the mail has moved to queues named to: domain (id), where nothing but this number and the broker's own queue list will find it.