Function sign_in_google_drive 

pub async fn sign_in_google_drive(
    key_service: &StoreKeys,
    store_name: &str,
    oauth_cancel: Receiver<bool>,
    clock: &dyn Clock,
) -> Result<String, SetupError>

Google Drive OAuth sign-in: authorize, find/create the store folder, save tokens to the keyring. Returns the folder id for the host to persist in its own config (coven never writes the host’s config).

Drives coven’s localhost-callback OAuth flow ([crate::oauth::authorize]), which binds a TCP port and opens the system browser. Gated on oauth-providers.