Peter Hoffmann

Over the past year we modernized ATLAS end to end, backend and frontend alike: the cohort design workbench the OHDSI medical research network has run for over a decade. The Java backend moved from Java 8 to Java 21 and Spring Boot 3: some 1,600 files, with a net 65,000 lines removed. The frontend is a ground-up rewrite in Vue 3 and TypeScript: 110k lines of source, gated on every pull request by coverage-enforced unit suites and an end-to-end fidelity check against the entire OHDSI Phenotype Library, running publicly at atlas-preview.ohdsi.org/atlas. The large majority of that code was written by coding agents, far more change than anyone could have read line by line. The platform and the verification harness are open source under the OHDSI GitHub org, end to end.

On the frontend rewrite I directed, reviewed, and accepted every change. When acceptance cannot mean reading every line, verification has to live somewhere else. The harness became the first reviewer, and I will show what it is made of: specs as the unit of delegation, the legacy implementation as a behavioral oracle, E2E suites and type gates as the merge criterion, and screenshot-driven iteration in place of pixel opinions. I will walk one real feature end to end and show the failure modes the harness caught, the ones it did not, and what I would gate differently today.

This talk is for engineers and leads who need to deliver more than their team can hand-write. You will leave knowing how to structure specs so agents can execute them, which verification gates can replace line review and which cannot, and how to tell whether your project fits this model (rewrites with a reference implementation) or does not.

Live instance: atlas-preview.ohdsi.org/atlas. All code: github.com/OHDSI/Atlas3.