Function lower_boolean_result_node 

pub fn lower_boolean_result_node(
    session: &mut LoweringSession<'_>,
    id: EntityId,
    frame: Transform,
) -> GeometryResult<NodeId>

Append one IfcBooleanResult (or clipping result) and return its node.

Both operands are lowered into the same session before the operation node is appended, which is exactly the ordering the append-only builder needs: every reference is already a prior node.