LegacyLift

THE PROBLEM Millions of lines of COBOL still run the world's payroll, insurance, and banking. The engineers who wrote them are retiring, the documentation is gone or wrong, and the code is so load-bearing that nobody dares touch it. AI coding tools can generate replacement code — but they leave teams without verifiable proof that the new code behaves identically to the old. Migration projects rarely fail because rewriting is hard. They fail because there is no safety net. THE SOLUTION LegacyLift is a four-stage modernization pipeline that turns "nobody dares touch it" into modernized, tested, documented code — with a human approval gate before anything risky happens. Stage 1 — Discovery: Bob's document understanding reads the COBOL and produces CODEBASE_BIBLE plus a MODULE_SPEC of numbered business rules (BR-01…12). Stage 2 — Safety net: we compile and run the real binary, capturing 36 golden fixtures across happy paths, boundaries, and negative inputs. A Maven/JUnit characterization suite replays every fixture, field for field. Stage 3 — Plan: three parallel subagents (plan drafter, risk mapper, effort estimator) produce a migration plan — then the pipeline stops and a human signs APPROVAL.md. Stage 4 — Execute one slice: the port is written and every fixture replayed. If a test fails, the migration is wrong — never the fixture. Expectations are never edited to go green. THE PROOF The safety net is validated by mutation testing: we injected four deliberate defects (signed vs. unsigned math, progressive vs. flat tax, truncation vs. ROUNDED, removed net-pay floor) — all four were caught. The COBOL oracle is pinned by SHA-256; changing one byte fails CI, because every fixture would be invalidated. Vacuous green is treated as red: a guard fails the suite if a stub ever claims to be implemented. RESULTS (all re-run, not from memory) 43/43 characterization tests · 12/12 business rules = 100% coverage · 36 golden fixtures · 4/4 mutation defects caught · 16/16 Bob unit tests · 42/42 end-to-end tests. The oracle is 1,475 lines of unmodified COBOL; PAYCALC (349 lines) is fully migrated; CLAIMS (1,126 lines) is staged as the next slice with ten documented landmines. TARGET USERS & INTERACTION Enterprise engineers and modernization teams holding critical legacy systems with no tests and no docs. `npm run dev` serves the workbench, API, and metrics dashboard on one port; the daily loop is four commands: build the oracle, capture behavior, replay it, measure rule coverage. WHAT MAKES IT UNIQUE Not a transformation engine — a safety-net layer that complements tools like watsonx Code Assistant. Three things stand out: proof via mutation testing (the tests demonstrably catch wrong code, not just pass), structural honesty (we state plainly that CLAIMS.cbl sits outside the measured coverage number rather than silently narrowing the denominator), and the human gate: AI proposes, people decide.