Problem\nDeriving a krdanta for dhatu ha\na~ (Adadi) with kvip yields hAn, but the expected stem is han.\n\n### Repro\n- Derive krdanta with dhatu ha\na~ (Adadi) and krt kvip.\n- Actual: hAn\n- Expected: han\n\n### Root cause\nRule 6.4.15 (dirgha) applies when the pratyaya is kvip, lengthening the upadha before later stages. This happens before any han-specific handling.\n\n### Proposed fix\nSkip 6.4.15 when the next pratyaya is kvip.\n\n### Test\ncargo test -p vidyut-prakriya kvip_han_stem