pub const SIGNATURE_PREFIX: usize = 34;Expand description
Prefix length of the signature-frame tail: the 1,642-byte wire format puts
418 header bytes before the nodes, and 418 = 6 × 64 + 34.
The first 384 header bytes fill six whole beats that the signer writes itself; the last 34 share beat 6 with node 0, so they go through the packer as its prefix.