- /duonglich appends a nhuan hint when the queried month is also that
lunar year's leap month and the exact leap date exists
- both commands append a caveat when the result falls in a lunar month
starting or ending on one of the seven razor-edge boundaries from
2072 on (new moon within ~2 minutes of UTC+7 midnight)
- freeze the verified 1800-2199 month structure as golden testdata so
a self-consistent engine change cannot silently shift boundaries
- close known-issues open questions 1 and 2