New /reports/cartes page surfaces a dashboard-style snapshot of the
reference month:
- 4 KPI cards (income / expenses / net / savings rate) showing MoM and
YoY deltas simultaneously, each with a 13-month sparkline highlighting
the reference month
- 12-month income vs expenses overlay chart (bars + net balance line)
- Top 5 category increases + top 5 decreases MoM, clickable through to
the category zoom report
- Budget adherence card: on-target count + 3 worst overruns with
progress bars
- Seasonality card: reference month vs same calendar month averaged
over the two previous years, with deviation indicator
All data is fetched in a single getCartesSnapshot() service call that
runs four queries concurrently (25-month flow, MoM category deltas,
budget-vs-actual, seasonality). Missing months are filled with zeroes
in the sparklines but preserved as null in the MoM/YoY deltas so the UI
can distinguish "no data" from "zero spend".
- Exported pure helpers: shiftMonth, defaultCartesReferencePeriod
- 13 vitest cases covering zero data, MoM/YoY computation, January
wrap-around, missing-month handling, division by zero for the
savings rate, seasonality with and without history, top mover sign
splitting and 5-cap
Note: src/components/reports/CompareReferenceMonthPicker.tsx is a
temporary duplicate — the canonical copy lives on the issue-96 branch
(refactor: compare report). Once both branches merge the content is
identical and git will dedupe. Keeping the local copy here means the
Cartes branch builds cleanly on main without depending on #96.
Closes#97
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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