GUID persistence — runtime calls these to save/load per-iframe instance GUIDs.
GUIDs survive page reloads: same iframe slot gets the same GUID.
Implementor decides storage backend and keying strategy
(e.g., localStorage keyed by iframe src or slot index).
GUID persistence — runtime calls these to save/load per-iframe instance GUIDs. GUIDs survive page reloads: same iframe slot gets the same GUID. Implementor decides storage backend and keying strategy (e.g., localStorage keyed by iframe src or slot index).