Function payload 

pub fn payload(
    tree: &str,
    gates: &str,
    platform: &str,
    inputs: &[(String, String)],
    canon: Option<&str>,
    producer: &str,
) -> String

The payload of an attestation, in the exact shape SPEC.md gives: tree, gates, platform, the input lines in spec order, canon, then the producer line, each followed by LF. The same inputs give the same bytes, so a re-run recognises its own block.