Function lower_set_directive 

pub(crate) fn lower_set_directive(
    document: &mut Document,
    root: NodeId,
    name: &str,
    args: &[SetArg],
    span: &SourceSpan,
    metadata: &mut DocumentMetadata,
    current_text_size_pt: &mut f64,
    diagnostics: &mut Vec<Diagnostic>,
)

Lower a #set name(...) directive into a Raw node carrying the resolved attribute payload. The split exists so the dispatch in Evaluator::evaluate only has to thread state through three directive-shaped helpers instead of one large match arm.