Function append_bibliography_entries 

fn append_bibliography_entries(
    document: &mut Document,
    bib_id: NodeId,
    bib_span: &SourceSpan,
    bibliography: &LoadedBibliography,
    numbers: &BTreeMap<String, usize>,
)

Append one rendered entry per cited key as children of the first [NodeKind::Bibliography] node, ordered by first-use citation number.

Each entry is a [NodeKind::Paragraph] carrying entry_number / entry_key attributes and one [NodeKind::Text] child with the format_entry text, so layout can render the list with [N] markers without re-reading BibTeX sources. Uncited records add nothing, and unresolved keys never made it into numbers, so the numbered entries always match the citation markers in the prose.