Toast
Brief feedback that disappears on its own. Never for something the user has to act on.
Anatomy
A title, an optional line of detail, and at most one action.
Arrival
For short confirmations that need no action. It stays readable above an open dialog.
Why
Entrance is the one place a spring bounce is allowed: an arrival nobody asked for has to earn attention. Stacking is z-70, above the modal, so a save that fails while a dialog is open is still readable.