· Browser
Credential-backed sign-in, and downloads that stay gated
A browser pane can sign in from a stored credential without the agent ever seeing it, and a download an agent triggers still needs a person.
An agent that needs a signed-in page has two bad options: be given the password, or be blocked. Realm fills the credential into the page itself. The agent drives the browser; it never receives the secret.
Downloads stay gated behind an explicit approval. A file arriving on disk because a page offered it is exactly the event that should not be automatic.