The legacy online simulation path still exported internal ACTIVE states as STATUS keywords, which EPANET 2 rejects. Preserve numeric settings and EPANET 3 output while passing the format through both exporters. Surface the original engine error inside the model transaction so failed runs roll back before result storage.
Regression guard: six failures reproduced on the deployed baseline, including native input validation. All 34 focused export, service and endpoint checks pass after the fix; the real project also returns native node and link results.
