Republish the raw undecodable message to subject, then drop it from this subscription.

The dead-lettered message carries the original payload and headers plus the provenance headers in DeadLetterHeaders.

subject must be captured by a stream. On JetStream the dead letter is published as a JetStream message, and the original is terminated only once the server has acknowledged storing it - so a dead letter that never lands cannot take the original down with it. The flip side is that a dead-letter subject with no stream behind it holds every undecodable message unacknowledged for redelivery, which subscribe and pull reject up front rather than let you discover one message at a time.

On core NATS there is no stream and no acknowledgement to wait for: the dead letter is a core publish, and reaches only whatever is listening on subject at that moment.