How to access args.filter value in the onBeforeTimeHeaderRender event of DayPilot Scheduler

I'm working with DayPilot Scheduler and need to filter events in the onBeforeTimeHeaderRender callback function. I need to access the current filter value that was set elsewhere in my application.

In my onEventFilter function, I'm using args.filter successfully:

onEventFilter: (args) => {
  if (Array.isArray(args.filter)) {
    args.visible = args.filter.length === 0 || args.filter.includes(args.e.data.customer);
  } else {
    args.visible = false;
  }
}

However, when I try to use the same filter in onBeforeTimeHeaderRender to calculate filtered sums, I can't seem to access the filter value:

onBeforeTimeHeaderRender: (args) => {
  if (args.header.level === 0 || args.header.level === 1) {
    const events = scheduler.events.forRange(args.header.start, args.header.end);

    // How do I access the same filter that was used in onEventFilter?
    // Is there a way to get args.filter here?

    const sum = events.reduce((acc, event) => acc + event.data.quantity, 0);
    args.header.html = `${args.header.text} ( ${sum.toString()} )`;
  }
}

Is there a way to access the current filter value in the onBeforeTimeHeaderRender event? I need to use the same filter to calculate sums for only the visible events.

Any help would be appreciated. Thanks!