asyncssh defaults to querying SSH_AUTH_SOCK even when client_keys are
provided. If the agent socket is stale or broken (common with forwarded
agents in Docker/NAS environments), this causes a ConnectionResetError
that crashes the connection before the dedicated key is even tried.
Set agent_path=None when dedicated compose-farm keys exist so asyncssh
skips the agent entirely. The agent fallback path (when no dedicated
keys exist) is unchanged.