NULLPTR

In 2026 Vietnam changed the tax rules for its household businesses, then changed them again. Search a café's VAT threshold today and you get 100 million, 500 million or 1 billion VND, each quoted from a real decree. Only one is in force. Plain AI search cannot tell which, because the outdated clause is still online and matches the question just as well. LexVi answers tax questions for household businesses with only the law in force on the date asked. A Muse Spark agent searches 3,586 provisions from 30 official documents and follows each clause's amendment chain. Before any answer is shown, it must pass two gates: code checks that every citation exists, applies on that date and is quoted word for word, then a second Spark call that judges whether each clause supports the claim. Failures go back to the agent with reasons; after three, the answer is flagged for an accountant instead of guessed. When a new decree is published, LexVi reads the PDF and tells the owner which clauses changed and what to do, with deadlines taken only from the text. On our 20-question test set (11 date traps), with the same model, plain RAG cited repealed law 3 times and found the right legal basis 14 times. LexVi: 0 and 20. Information with citations, not tax advice.