Make a file importer safe to rerun

For [INPUT FORMAT], [TARGET SCHEMA] and [IMPORT RULES], design or implement an idempotent importer within the supplied repository. Define stable record identity, validation, dry-run output, transaction boundaries and the result of retrying after a partial failure. Provide code or pseudocode, tests for duplicates and malformed rows, and a rollback procedure. Do not write to live data without separate approval. Check that two identical runs produce the same final records and that a corrected source row updates only according to an explicit rule.