== Datasource
app_open events will be written to `event.product_metrics_app_base` when T423720 and T423721 are finished
Need to migrate / integrate with existing data in @SNowick_WMF's tables (see [[ https://superset.wikimedia.org/superset/dashboard/iOS_Monthly_Metrics_Dashboard/?native_filters_key=_hDN0uRr48MYLkULD7RWyoP6CzGEtb9kNaWflIJJMrmWelrYwnBVvbNGKy7pz4R0 | datasets in dashboard ]])
== Definition
User: uniquely identified by app install id in imported events (see above)
App Open: anytime the screen of the app is in the foreground of the user's device (not backgrounded or displayed as a secondary widget - see tasks mentioned above for details).
DAU: Daily active user count. How many unique Users send the "app open" event on a given day?
Metric: Compute DAU at the end of each day, UTC time
NOTE: if it can be delivered later in the day, that's better for sustainability, see T384166
(for this metric it seems like it's not a problem to delay the metric results)