Function emit_unresolved_reference 

pub fn emit_unresolved_reference(
    builder: &mut GreenNodeBuilder<'_>,
    is_image: bool,
    text_content: &str,
    label_suffix: Option<&str>,
    config: &ParserOptions,
    suppress_footnote_refs: bool,
)

Emit an UNRESOLVED_REFERENCE node for a Pandoc bracket-shape pattern whose label didn’t resolve. The wrapper covers the original bracket bytes; the inner text recurses through normal inline parsing (with inner-link suppression so a stray inner inline link doesn’t reorder semantics relative to pandoc-native).

source is text[start..end] — the full bracket-shape pattern. text_content is the inner text between the outer [ and ] (the bytes used for inline recursion). label_suffix carries the [label] / [] suffix bytes verbatim, or None for shortcut form.