Function norm_add_var

crates/kernel/src/level.rs:329–331

(s: &mut NormLevel, idx: u64, k: u64, path: &[u64])

      Err(pos) => self.var.insert(pos, VarNode { idx, offset: k }),
    }
  }
}

/// Canonical form: a map from imax-paths (sorted param indices representing
/// the conditioning chain) to nodes tracking constant offsets and variable
/// contributions.