Function rewrite_references 

fn rewrite_references(
    document: &mut Document,
    labels: &BTreeMap<String, LabelTarget>,
    bib_keys: &BTreeSet<String>,
    diagnostics: &mut Vec<Diagnostic>,
) -> bool

Rewrite each Reference node’s text attribute to point at its target. Returns true if any node was mutated this iteration: callers use that signal to drive the §6 stage 3 fixpoint loop.