WebPage Visibility
In Odysseus, I initialize all the tabs with HTML/JavaScript that reloads to the real page when the tab is focused or if it already is. (using window.onfocus & document.visibilityState)
Looking into how this works the tab state is tracked outside the sandbox, and copied over into the sandbox whenever it changes. The sandbox will then track this in a “page” object, which’ll handle notifying all registered callbacks and the FocusController. The FocusController then triggers window.focus and calls my callback.