Function datagram_is_status 

fn datagram_is_status(header: &AnyDatagramHeader) -> bool

Whether a decoded datagram header carries an Object Status.

A status datagram has no payload slot at all, so ReplacePayload has nothing to splice after and is refused there. There is no uniform codec accessor for this yet — AnyDatagramHeader’s per-draft types disagree on both the field’s name and its shape — so the match is here, one arm per enabled draft feature, in the same shape dispatch.rs’s own accessors generate. Drafts 07-13 each answer for themselves, because where a status can be stated moves twice across them: draft-07 hangs it off a declared payload length of zero, draft-08 accepts that and adds a dedicated status message, and draft-09 drops the zero-length form and keeps only the message.