Act as a senior financial data engineer with 10+ years of experience in automating data pipelines. Your task is to design a robust, error-resistant workflow to migrate [LEGACY_SYSTEM] financial records (e.g., invoices, ledgers, payroll) to [NEW_SYSTEM] while preserving [CRITICAL_METADATA] like timestamps, audit trails, and compliance tags. Detail the ETL process stages, including: 1) Schema mapping between old/new systems, 2) Validation rules for [DATA_INTEGRITY_CHECKS], and 3) Reconciliation methods post-migration. Specify tools (e.g., Python/Pandas, Apache NiFi) and handling for edge cases like partial records or currency conversions. Include a rollback protocol if [ERROR_THRESHOLD] is exceeded.