Full time-domain audit (three shipped date bugs prompted it) found one
root cause and two latent travel defects, all now fixed:
Day-stepping used add(Duration(days: 1)), which shifts the absolute
instant by exactly 86400s — documented Dart behavior (sdk#47666), so
crossing a DST transition drifted the wall hour by +-1h permanently
for the rest of the candidate scan (verified: 2026-03-28 07:30
Europe/Madrid + "1 day" = 08:30). The native Calendar engine preserves
wall time, and the single-authority fix made the drifted Dart verdict
win. Candidates now advance by calendar reconstruction (_siguienteDia:
DateTime(y, m, d+1, hora, minuto)), the same wall-clock-preserving
semantics as Calendar.add(DAY_OF_YEAR, 1) plus AOSP DeskClock's
defensive hour/minute re-assertion, keeping both engines in agreement
through any transition.
Instant-valued fields (snoozeHasta/snoozeOrigen/proximaEjecucion/
ultimaEjecucionGestionada/creadaEn/actualizadaEn) serialized as
offset-less local ISO, so re-parsing after a device timezone change
reinterpreted the same wall fields as a different instant. They now
serialize as UTC ("Z"); reads normalize to local, and legacy
offset-less payloads parse identically — no migration. fechaUnica
stays local on purpose: it is a wall-clock date.
One-shot alarms sent fechaUnica's midnight epoch to the native side,
whose boot/travel re-arm derives the calendar day back from it in the
CURRENT zone — a westward shift rolled the date to the previous day.
The channel now anchors the date at local noon, keeping it stable
across real-world zone shifts.
Property tests lock the no-drift guarantee (400 daily / 200 weekday
iterations must all land exactly at hora:minuto — on DST-observing
dev machines this crosses real transitions), plus UTC round-trip,
legacy-payload compatibility, and wall-date preservation tests.
FreeTLab
Javier Bautista Fernández