An Agentic Workflow for Legacy HPC Modernization: Converting the Two-Electron-Integral Core of GAMESS

TL;DR - A three-role agentic workflow modernized 56,448 lines of GAMESS from Fortran 77 to Fortran 2008 while preserving canonical outputs bit-for-bit. It demonstrates that exact domain-specific verification can enable safe, production-scale delegation of legacy HPC maintenance.

• Converted 12 files and 225 electron-repulsion-integral subroutines.
• Claude Code agents worked in isolated worktrees under a version-controlled specification they authored and revised.
• Human oversight was limited to gates, with safe delegation bounded by the verification oracle’s coverage.
• All files passed 51 calculations and Jenkins CI; 612 test runs produced zero chemistry-relevant differences.