pub fn submit_signing_payload(hash: &HopHash, submit_timestamp: u64) -> [u8; 32]Expand description
Compute the 32-byte payload signed at hop_submit time.
The runtime pallet re-derives this exact byte sequence to verify the
signature on-chain, so the construction must remain byte-identical to the
pallet’s signing_payload(data, submit_timestamp):
blake2_256(HOP_SUBMIT_CONTEXT || blake2_256(data) || submit_timestamp.to_le_bytes()).