Live bill INV-2608-T5EDD-00116 carried billedat 2026-08-05T12:49:28Z beside
receivedat 2026-08-05T07:19:28Z — the sale appearing to have been rung five and
a half hours after the back office received it. Exactly the IST offset, on every
bill.
Nothing was lying. DateTime.toIso8601String() on a local time emits no zone
marker at all, and Go's time.Parse fills that silence with UTC, so a Coimbatore
wall clock was recorded as though it had been read in London.
The daily figures survived by luck: businessdate is derived from the wall clock
either way, and the wall clock was always the till's own, so a day's takings
landed on the right day even while the instant was wrong. Anything comparing
billedat against real time did not.
Formatters.isoWithOffset attaches the offset, which fixes both readings at once
— the instant parses correctly and the local date still formats correctly. The
minutes come from the real offset rather than being assumed zero, because India
is +05:30 and a whole-hour implementation would be wrong in a way that looks
almost right.
Applied to all six timestamps the till sends. date_of_birth is left alone: a
birthday is a date, not an instant, and giving it a zone would be meaningless.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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