A Duration is an absolute span, so stepping a local DateTime by
Duration(days: 1) moves 23 or 25 hours across a DST boundary and lands on
the wrong wall-clock day. Under Europe/Warsaw, spring-forward 2026-03-29:
lastCompleteDay(2026-03-30) -> 2026-03-28 23:00, the day before
yesterday, not yesterday
weeksAgo: 1 from 2026-04-01 -> 2026-03-24 23:00, a Tuesday, so the
wrong ISO week entirely
a 03-27..03-31 period -> emits four day keys, silently dropping
2026-03-31
The Python half computes all three correctly, because timedelta on a date
has no clock to drift against. So for about two weeks a year the phone and
the PC would report different averages for the same log -- exactly the kind
of device-local divergence the shared-source-of-truth rule exists to stop.
Passing out-of-range components to DateTime's constructor normalizes on the
calendar (day 0 is the previous month's last day), which is what timedelta
already does. The same fix goes to day_status_service's streak walker: it
had the identical pattern and predates this feature, so a streak that
spanned the clock change could break when it should have held.
None of the existing tests could see any of this -- every fixture date sits
in a DST-free span -- so the regression tests use dates that straddle
2026-03-29 and assert on the calendar day rather than the DateTime, which
keeps them meaningful whatever zone the runner is in. Verified they fail
against the old arithmetic before fixing it.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DjJqpcEsaV5WRhPXyxCThd
The calendar already said which individual days went over budget, but not
whether the week as a whole did. A run of small overages reads as four
harmless yellow squares; averaged, it is the thing that actually moves the
needle.
Three rules are load-bearing, and are documented in CLAUDE.md because getting
any of them wrong silently changes what "under budget" means:
- The denominator is logged days, not elapsed days. An unlogged day is not a
zero-kcal day, and averaging gaps in as zeros would make a badly-tracked
week look like the best week of the year.
- The yardstick is the mean of the per-day budgets over those same days,
resolved through BudgetSchedule -- never today's budget, which would
retroactively reclassify past weeks on every budget edit.
- Today is excluded. A half-logged today drags the mean far enough to flip
the band, so every period ends at yesterday.
Band boundaries reuse the calendar's own OVER_BUDGET_YELLOW_CEILING by
import rather than by copy, so a period and its days can never disagree
about what "over" means; that constant loses its underscore to say so.
The MCP get_averages tool returns the average and the band but drops the
average budget, keeping the module's existing invariant that the budget
number never leaves this machine. The CLI, the gate and the phone all show
both, since it is hidden from the network, not from the user.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DjJqpcEsaV5WRhPXyxCThd
