Calls listener whenever the status may have changed: the extension
announced itself (installed or updated while the page is open), or a
request failed with AppMissing/AppOutdated (the app was removed or
needs an update). The listener receives a fresh status; it is not
called for the state at subscription time, so call status() once
yourself. Returns an unsubscribe function (safe to call twice).
Calls
listenerwhenever the status may have changed: the extension announced itself (installed or updated while the page is open), or a request failed withAppMissing/AppOutdated(the app was removed or needs an update). The listener receives a fresh status; it is not called for the state at subscription time, so callstatus()once yourself. Returns an unsubscribe function (safe to call twice).