Reconciliation that reports breaks the day they happen

The problem

Reconciliation ran monthly and compared totals. A break that started on the third of the month surfaced on the first of the next one, by which point the cause was buried under four weeks of writes.

The approach

We moved reconciliation to a daily job comparing at the transaction level rather than the total, and made every write path idempotent so a retry could not itself create a break. The daily report names the first divergent transaction rather than a delta.