`instant.toISOString().slice(0, 10)` and parsing a key back as UTC
midnight are the idioms behind every day-boundary fix this year: the
evening west of UTC and the small hours east of it land on the
neighbouring day. A new rule, healthlog/no-utc-day-key, refuses them in
src/ outside src/lib/tz and tests, and refuses a disable directive for
itself that is not next-line or gives no reason.
The time zone module now names every legitimate form: userDayKey for a
person's day, dateOnlyKey / dateOnlyAtNoonUtc / dayKeyAsUtcMidnight for
date-only values and day labels, daysBetweenDateKeys / weekdayOfDateKey /
isCalendarDateKey / statedDateKey for key arithmetic and parsing.
Of the 133 sites the rule found, 84 are gone. Most moved onto a named
helper with no change in behaviour; these changed behaviour:
- cycle calendar, insights, Coach snapshot and prediction refresh start
their lookbacks at the first instant of the user's day
- a model-transcribed date like "June 10, 2026" no longer lands a day
early in a process east of UTC (documents and lab scans)
- a custom report range covers exactly the picked days in the profile
zone instead of starting the evening before west of UTC
- date-of-birth pickers cap at the user's today, not the UTC one
- an allergy onset date is stored at noon UTC like other date-only values
- the report's cycle summary, the Coach's usual BP range and the intake
projector's rollup recompute use the user's day
- vaccination dates render as dates instead of the previous evening
49 remain, each with its reason on the line above: 39 UTC by design (15
file name stamps, rollup and object keys, the UTC-day score engines) and
10 marked baseline. A guard test requires a classified reason on every
directive and holds the baseline to a ceiling that only goes down.
The status assessments folded their recent days, weeks, months and years on
Berlin days whatever the user's zone, the mood and cycle crosstabs keyed
their metric days in Berlin, the resting-pulse proxy defaulted to Berlin
days, the briefing's opener rotated at Berlin midnight, and every
assessment prompt labelled today's date as Berlin's. They now use the
user's zone. Rollup months and years are labelled by their UTC start,
which is how they are cut; read in a zone west of UTC the label named the
month before.
"Europe/Berlin" was written out in some eighty places. DEFAULT_TIMEZONE in
lib/tz/format is now the one definition: the second copy in mood/date-key,
DISPLAY_TIMEZONE, the Berlin-only day key helpers and the per-route copies
are gone. An in-repo lint rule rejects the literal outside lib/tz and
tests; four areas another change owns are listed as pending.
A GET must not have side effects — api-handler.ts says so next to
READ_HTTP_METHODS, where an MCP-audience token is admitted on the safe
methods precisely because they are assumed to write nothing. Three routes
broke that: the sync handshake bumped User.lastSyncedAt, the achievements
read inserted unlock rows, and the cycle calendar fired a discarded promise
at the forecast cache so a failed write left no trace anywhere.
Each write moves to the place that causes it.
The sync checkpoint is now stamped by the batch ingest endpoints for
measurements, mood and intakes. The handshake reports it. That also fixes
the watermark: the checkpoint used to advance past a window the client had
not drained, and a client trusting it would skip that window. It can only
trail a real sync now.
The unlock rows move to a nightly achievement-unlock-sweep. The badge grid
never needed them — unlocked comes from the live metrics and the completion
date is derived — so the payload is unchanged; the rows pin that date and
carry it into the backup, and the sweep reaches accounts that never open
the page.
The cycle forecast moves to a nightly cycle-prediction-refresh. The
CyclePrediction row is not a cache of a read: it is the index the reminder
cron scans, so which reminders an account received depended on whether
somebody had opened the calendar. persistPredictionCache no longer
swallows its errors either — the job reports them.
Marc-André Bombeck