Integration: Reconciliation (3-part)

Problem: Integration - Reconciliation (3 parts) Implement a reconciliation/integration task with three parts: Part 1 is quick. Part 2 is large and verbose; you must implement step-by-step per part. Part 3 may be only partially completed under time. Note: The post does not include the data model, IO format, reconciliation rules, or constraints, so it cannot be reconstructed into an answerable coding prompt and is omitted.