Optional ReadonlyexpirySession expiry timestamp in ISO 8601 format.
Optional ReadonlyloginEpoch-ms deadline before which automatic re-logins are refused.
Optional ReadonlypasswordAccount password.
Optional ReadonlyusernameAccount username (email).
Session material both dialects persist through the host's SettingManager: credentials, expiry, and the login-backoff gate (previously undeclared — a host clearing every declared key left the backoff behind).