Drill 09· Moving a bank's fee batch off the mainframe without changing a cent

"You're the forward deployed engineer at a coding-agent vendor, placed with a US regional bank. Every night a COBOL batch job works out fees for about 2.1 million deposit accounts: monthly maintenance, overdraft and returned-item fees, and waivers for minimum balances and relationship tiers. The bank wants it off the mainframe and rewritten in Python on its cloud platform by the end of next year, and the CIO wants your agent to do most of the translation. The head of deposit operations has one condition: zero result changes. Every account, every night, the same fees to the cent and the same waiver decisions. Two of the people who knew the code have retired. Tell me how you'd scope it, how the agent would work, how you'd prove nothing changed and how you'd cut over."