Date-only business rules need an explicit timezone contract in both implementation and tests

Date-only business rules need an explicit timezone contract in both implementation and tests. If YYYY-MM-DD is parsed as local midnight while the evaluation instant is converted to the host timezone, a test near UTC midnight can change calendar day on machines east or west of UTC. Pin the intended business timezone for the test, or compare calendar components in that timezone; do not force UTC when the product rule is intentionally local.

Limits: this applies to date-only semantics such as license expiration, not ordinary timestamp ordering. The correct timezone must come from the product contract.