Function useAppVisible

Whether the player can see this app right now (MICA-294): a device is open, its screen is showing apps — no lock screen or dead battery over it — and this app is the one in front. Phone and tablet alike.

onAppForeground answers a different question. It fires when the app comes to the front, and putting the phone away does not send the app anywhere: it is still the current app, so nothing arrives when the phone goes down, and an app kept mounted across the close gets no second foreground when it comes back up. An app that polls — Places reads live positions every few seconds — cannot tell from it that nobody is looking. This can.

Use onAppForeground to load, and this to decide whether to keep doing something:

const visible = useAppVisible('places');
$effect(() => {
  if (!$visible) return;
  void refresh();
  return every(5000, () => void refresh());
});
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The app names itself, as it does for onAppForeground, and can only ever ask about itself: a sandboxed add-on's id is pinned by the shell, whatever it sends. Implicit, like onAppForeground: an app knowing whether it is on screen discloses nothing about any other. In an add-on it reads false until the shell's first answer arrives.