Three correctness issues in `summarize()` / `trendSlope()` /
`weeklyAverages()` that the discovery audit reproduced:
1. **`summarize` and `trendSlope` used different time anchors.** The
averages (`avg7`, `avg30`) snapped to `Date.now()`, while the slopes
(`slope7`, `slope30`, `slope90`) snapped to the latest point in the
series. A stale series (no readings for weeks) reported a slope from
old data even though the dashboard tile correctly hid the average.
Both surfaces now use `Date.now()` as the cutoff, so a stale series
returns `null` from every windowed stat consistently.
2. **`summarize([])` returned `{ min: 0, max: 0, mean: 0 }`.** Those
sentinels leaked into chart axes (Y-axis collapsed onto zero) and
into AI-prompt feature bundles where the generator treated the zero
as a real reading. Empty input now returns `null` for all three
fields. The `DataSummary` type widens accordingly; the dashboard
already null-checks the optional fields, so no UI regression.
3. **`weeklyAverages()` used system-local `Date.getDay()` /
`getDate()`.** On a UTC server (which is what the production
container runs as) a Sunday-evening Berlin reading bucketed into
the next week. Now the ISO-Monday key is computed via
`Intl.DateTimeFormat({ timeZone: "Europe/Berlin" })`, so the bucket
lines up with how the user perceives "this week".
`pairByTimestamp` keeps the greedy nearest-match heuristic — adding
JSDoc that documents the limitation and the conditions under which a
Hungarian-style match would matter (sparse health data is well below
that bar).
Tests: 371 → 384 (+13). Two new direct regression tests:
- `weeklyAverages` Sunday-evening-Berlin bucket goes to the *previous*
Monday.
- `summarize` with all readings 100 days old returns `null` for every
windowed stat (no false trend on stale data).
Plus tightened the empty-summarize assertions.
Co-authored-by: Marc-André Bombeck <noreply@anthropic.com>
HealthLog — personal health-tracking PWA with weight, blood pressure,
pulse, mood tracking, medication compliance, Withings integration,
doctor report PDF export, and Dracula-themed UI.
