Heirloom: Legacy Knowledge You Can Prove

Critical legacy systems often outlive the people who fully understand them. Their behavior is scattered across screen maps, transaction handlers, business programs and database calls. A conventional rewrite can produce cleaner code while quietly changing the job the software was built to perform. Heirloom addresses that risk by making modernization traceable, reviewable, and honest. Heirloom begins with the legacy source itself: IBM's CICS GenApp BMS maps and COBOL programs at a pinned commit. It extracts a structured catalogue of screens, fields, actions, program links, constraints, and evidence references, then reconstructs the original 24-by-80 green screens so reviewers can see the workflow that existed before modernization. A focused modern web application implements the verified customer and motor-policy tasks using Python, SQLite, semantic HTML, CSS, and browser-native JavaScript. The key difference is the verification loop. Deterministic checks compare exact facts such as task availability, field names, maximum lengths, and input behavior. IBM Bob then reviews workflow meaning against cited COBOL lines, including who assigns identifiers, which fields identify a policy, and whether an update must retrieve a record before editing. Our first modern build passed 10/10 application tests and 14/14 structural checks, yet this review found six workflow gaps. Each became a targeted repair with a regression check that failed before and passes after, and Bob's independent final review returned READY. Uncertain behavior remains clearly labelled instead of being invented. Heirloom is designed for modernization teams, engineers, business analysts, auditors, and product owners responsible for high-value legacy applications. They can explore the reconstructed screens, inspect source-linked evidence, use the modern customer and policy workspace, and review machine-readable verification results; 118 checks run on every push. Judges can follow the same evidence trail at https://heirloom.54-154-121-30.sslip.io without needing access to a running mainframe. For this hackathon, the legacy application was read from source; no mainframe was run. The demonstration records are explicitly invented. The first modern implementation is preserved at a Git tag, and reports and screenshots record every check before and after repair. Heirloom does not pretend to modernize an entire enterprise system in one leap. It demonstrates a safer pattern: understand first, preserve evidence, modernize a bounded workflow, test exact facts, review meaning, and repair only what the source can prove.