Function hash_request 

pub fn hash_request(
    method: &Method,
    path: &str,
    content_type: Option<&str>,
    body: &[u8],
) -> [u8; 32]

Stable fingerprint of a request: SHA-256 over method, path + query, content-type, and body bytes. Used to detect when a duplicate key is reused with a different payload (the conflict case the draft spec calls out). The path argument should include the query string so modifier-style flags (?dry_run=true, ?confirm=true) don’t collide — the middleware passes Uri::path_and_query for that reason.