Use when
- A message should be encountered before the page H1 but is not the page's main task content.
- A service problem, deadline, overdue action, or elsewhere-in-service event affects the user's next interpretation of the page.
- A user has just completed an action on a previous page and needs confirmation while continuing the same service journey.
- One concise page-flow notice is enough, with no modal decision and no broad cross-section persistence.