Function render_event_band 

pub fn render_event_band(
    ui: &mut Ui,
    events: &[Marker],
    visible_data: &[Bar],
    coords: &ChartMapping,
    baseline: f32,
) -> Option<String>

Draws host-supplied event badges just above baseline, using the chart’s time mapping. An event between bars uses the first bar at or after its time; whitespace extrapolates the most common positive spacing among the outermost 16 bars. Colliding badges stack upward. Returns the clicked event ID; callers handle that action before starting a chart drag. The badges use the event’s colour, text and tooltip, without assigning any market meaning to them.