gmt-timezone

Use convertPlainDateTimeToZoned from @northguild/gmt with an IANA zone id like America/New_York. Pass a disambiguation option (compatible, earlier, later, or reject) to control how DST gaps and overlaps are resolved.

addZoned accepts a disambiguation option, but it only affects fall-back overlaps, not spring-forward gaps. For gap safety, use convertPlainDateTimeToZoned with the reject mode, or classify the wall time first with classifyLocal.

An offset like -05:00 is a fixed shift and cannot observe DST rules, while an IANA zone like America/New_York carries full transition history. Use toOffsetInstant to split a timestamp into instant, offset, and optional zone when both are needed.

Use floorToZone or bucketRange with the target IANA zone so buckets follow local calendar boundaries. Days that spring forward are 23 hours and fall-back days are 25, which keeps daily aggregates aligned instead of forcing uniform 24-hour UTC buckets.

roundZoned follows TC39 ZonedDateTime.round, which rounds the wall clock and re-resolves it in the zone, so trunc mode can move forward across a DST transition. Use floorToZone or startOfZoned with no options to get a true boundary.

Yes, but only addZoned, subtractZoned, diffZoned, convertZonedToCalendar, and zoned interval functions accept the [u-ca=...] annotation, which GMT places before the timezone bracket. Always produce these strings with convertZonedToCalendar.