The two code paths
The engine runs against EMSA THETIS-MRV two independent ways: a calculation-only path that reads the CSV directly into the calculators, and a full-stack path that persists and rehydrates every row through the production handlers a customer would hit. Both paths must produce the same fleet-aggregate penalty to ±0.0000% or the build fails.
Fixture pinning
Every regulatory constant lives in one of 9 JSON fixtures, each entry carrying the Official Journal article reference inline: Cf and LCV per fuel, the FuelEU target line (Reg. (EU) 2023/1805 Article 4(2)), the penalty rate (Annex IV: €2,400 per tonne VLSFO-equivalent), the EU ETS phase-in (Directive 2003/87/EC Article 3gb), and the IMO CII reference line (MEPC.354(78)). Constants embedded in a calculator class fail a static check.
EMSA reconciliation
EMSA publishes a yearly emission report for every vessel above 5,000 GT calling at an EU port (Reg. (EU) 2015/757 Article 21). The 2023 dataset contains 12,829 vessels. Of those, 12,637 carry the fuel and distance data needed to project a 2026 FuelEU penalty; 11,928 are in deficit at the 2026 target line. Rows without sufficient public detail are surfaced as a count, never as imputed numbers.
Audit trail
Every euro on the verifier-ready report traces back to the fuel record, the BDN, the Cf and LCV, the calculator class, and the engine version that produced it. Citation strings include the Official Journal reference and article number.
What this does not prove
Two-path reconciliation proves the engine produces consistent, citation-grounded numbers. It does not prove regulatory correctness — that judgement belongs to an accredited verifier under Reg. (EU) 2015/757 Article 11.