Spec a bank and ledger CSV reconciliation script

Every month your finance team checks the bank statement against the company ledger by hand, line by line. You want an agent to write a Python script that reads both CSV exports and writes a third CSV of the transactions that do not match.

Write the spec you would hand the agent.

What you know:

• bank.csv has Date like 03/14/2026, a signed Amount with debits negative, and Description
• ledger.csv has posted_on like 2026-03-14, a positive amount, direction as debit or credit, a 6-character ref and memo
• a pair matches when the dates and amounts agree and the bank description contains the ledger ref
• fields have stray spaces, and the same coffee order can appear twice on one day for the same amount
• finance re-runs the script after fixing entries, and keeps every output

Then, in a few sentences: what does "write a script to reconcile these CSVs" get wrong?