Function sign_lan_jekt 

pub fn sign_lan_jekt(
    private_key: &[u8],
    msgid: &str,
    source_agent: &str,
    target_agent: &str,
    ts_secs: i64,
    message: &str,
) -> Option<String>

Sign a jekt with the sending agent’s own LAN private key (read from its AGENTMUX_LAN_KEY process env var, mirroring sign_jekt’s AGENTMUX_JEKT_KEY — called client-side, inside agentmux-mcp, never server-side). private_key must be exactly 32 bytes (the seed generate_lan_keypair produced) — returns None on any other length rather than panicking, same “missing/malformed key must never block sending” policy sign_jekt’s callers already rely on.