You're right that if an attacker can access the proxy vault then by definition they'd similarly be able to proxy requests through it to get data back but at least AV prevents them from gaining direct access to begin with (the key to access the proxy vault itself can also be made ephemeral, scoped to a particular agent run). I'd also note that you'd want to lockdown the networking around AV so it isn't just exposed to the public internet.

The general idea is that we're converging as an industry on credential brokering as one type of layered defense mechanism for agents: https://infisical.com/blog/agent-vault-the-open-source-crede...