Function compile 

pub fn compile(
    operators: &[Arc<dyn RowJacobianOperator>],
    row_hess: &dyn RowHessian,
    ordering: &[BlockOrder],
) -> Result<CompiledBlocks, CompilerError>

Compile a sequence of row-Jacobian operators against a shared row Hessian. Walks ordering left-to-right, residualising each block against the cumulative anchor in the H_i-weighted row metric, then performs a joint-design audit and emits one CompiledBlock per input (in the same order as operators).

ordering parallels operators and supplies the semantic label for each block. The compiler treats ordering[i] purely as metadata — the position i is the residualisation order.