Errors
unauthenticated
No browser session was presented with this request.
unauthenticated is a 401 from the browser session route when the request carries no usable session at all — no cookie, or one that no longer resolves to a signed-in principal. It is the "never signed in" case; a session that existed and lapsed returns session_expired instead, and an API key that fails returns authentication_failed.
Recovery guidance
Send the user through sign-in and retry once a session exists. This is the expected response when an anonymous browser asks who it is, so treat it as a normal signed-out signal rather than a failure worth surfacing as an error. Retrying without establishing a session will return the same result.