GPU porting agent speeds weather code 5.1x

An AI-assisted workflow ported 162 kernels in the 250,000-plus-line CReSS weather simulator and delivered a 5.1x application speedup, while catching numerical discrepancies in five kernels. The validation-centric GPU-porting study used real typhoon states, element-wise comparisons, and application-level checks rather than trusting generated code on compilation alone. For teams modernizing scientific Fortran, the useful number is not the speedup by itself: it is the five defects that a benchmark-only workflow would have shipped; pair the pattern with GPU correctness gates that expose lenient kernel checks before an agent touches production science.