Function check_option_map 

pub fn check_option_map(
    cx: &mut Cx,
    expr: &Expr,
    fields: Vec<OptionFieldSpec>,
    extra: TableExtraPolicy,
) -> Result<ShapeMatch>

Check an option-map expression against field specs and an extra-key policy.

This is intentionally a thin wrapper around TableShape: it gives option parsers a domain-named entry point while preserving the same match scoring, captures, and diagnostics as the table grammar.