Function
true when the app was launched from the home screen
Two signals, because neither covers the field on its own. display-mode: standalone is the standard one every Chromium browser answers. Safari's own
navigator.standalone predates that media query and is still the reliable
signal on iOS, so both are consulted and either one is enough.
This is the definition of "already installed" for the whole app: the install guide and the install prompt both withdraw on it, and they must withdraw on the same evidence, or a learner ends up being offered one of them after having done it.
It reads window and navigator, so it SHALL only be called from the
client, and never while rendering on the server.
Whether the app is already running from the home screen rather than in a browser tab.