in src/trace/trace_context.rs [457:465]
fn push_active_span(&mut self, span: &SpanObject) -> SpanUid {
let uid = self.generate_span_uid();
self.primary_endpoint_name = span.operation_name.clone();
let mut stack = self.active_span_stack_mut();
stack.push(ActiveSpan::new(uid, span.span_id));
uid
}