Function phase_symbol_tables 

pub fn phase_symbol_tables(
    groups: &BTreeMap<String, Vec<usize>>,
    kinds: &BTreeMap<String, UnitKind>,
    parsed: &[ParsedFile],
    errors: &mut ErrorSink,
) -> HashMap<String, UnitTable>

Phase 4: build each production unit’s combined symbol table from its files, pushing any table-construction errors into errors.