Agent forwarding is not the agent itself. A local agent can answer authentication requests without sending the private key to the server. Forwarding additionally makes that service reachable through a socket on a remote host. Keeping key material local therefore does not mean keeping its authentication capability local. ...
An SSH agent provides signing operations for public-key authentication. For ordinary software keys, loading an encrypted private key unlocks material that the agent can then use without asking for the file passphrase on every connection. Clients receive public identities and signatures, not an exported private key through the normal agent protocol. Hardware-backed identities are different: the authenticator can retain the private key and require touch or verification. ...
Record the expected fingerprint, use a deliberate StrictHostKeyChecking policy, and treat changes as an incident until explained.
SSH key hygiene starts with knowing which credential grants which access, who owns it, and how that access ends. A key comment helps people maintain an inventory, but it is not an authenticated owner record or an authorization rule. Track fingerprints alongside accountable owners, intended accounts, permitted operations, and a removal plan. Generating a modern key is only the beginning. ...