Function inject_current_span_into 

pub fn inject_current_span_into(headers: &mut HeaderMap)

Inject the current tracing::Span’s OTel context into headers.

Uses the propagator installed by crate::observability::init. If no propagator was installed (e.g. in a test that didn’t run init), this is a no-op — the global getter returns a no-op propagator by default.