Function read_client_key_as_pem 

fn read_client_key_as_pem(path: &Path) -> Result<String>

Return PEM bytes that reqwest::Identity::from_pem accepts. FOOTGUN: the agent’s client key is the host SSH key, which is OpenSSH format - neither reqwest nor rustls parses it. We extract the 32-byte ed25519 seed and re-emit as PKCS#8 PEM. PEM inputs pass through unchanged.