Aggregate Reconciliation

Check that detail rows add up to the totals a summary declares, group by group. Sums are computed exactly on the decimal text, never through floating point: a float sum of 0.10 and 0.20 is 0.30000000000000004, so a tool built on one reports a false mismatch on the group that actually balances. Reports mismatches with the exact difference, groups with detail and no declared total, and totals with no detail at all.