Backlog: price-history direction — P0 relay archive (start now) → P1 Favourites Trends graph → P2 avg/min-max overlay → P3 prediction arrow + widget sparkline

BACKLOG.md

@@ -9,6 +9,17 @@ Status: TODO / IN PROGRESS / DONE / BLOCKED.
 
 ---
 
+## P0 — Next build
+
+- [ ] **Price history archive (start now — warm the data for Trends)** — relay-api
+  appends one daily snapshot (digest-change-triggered, once per calendar day) using
+  the existing `relay_snapshot.py` shape; prune to ~90 days (~18 MB). No UI
+  dependency: accumulating TODAY means the Trends graph launches with weeks of real
+  history instead of an empty chart. Optional first-weeks tweak: hourly snapshots to
+  build history faster, then settle to daily. Later add
+  `/api/v1/history?station=&fuel=&days=` (keyless, X-Client-tagged like
+  `/api/v1/stations`).
+
 ## P1 — Soon
 
 - [x] **Siri: "Cheapest [fuel] near me"** — `AppShortcutsProvider` + `CheapestFuelIntent`
@@ -23,6 +34,15 @@ Status: TODO / IN PROGRESS / DONE / BLOCKED.
   Directions-to-cheapest `caadf18` + spoken hand-off `aed99e3`.*
 - [ ] **Siri: "Closest [fuel] station"** — same plumbing as cheapest, sort by
   distance instead of price. Free second phrase in the same `AppShortcutsProvider`.
+- [ ] **Favourites Trends graph** — price history chart for starred stations.
+  Swift Charts (iOS 26 target) line chart in the Favourites tab; one series per
+  favourite, fuel-scoped (station, fuel) pairs map 1:1 to the archive. Default =
+  absolute price lines; toggle "vs cheapest favourite" re-baselines to 0 as signed
+  pence (mirrors the Cheapest/Closest delta pattern users already know). Reuse the
+  capsule fuel picker; range control 7/30/90 days; respects the price-display
+  toggle; honest empty-state copy in Localizable.strings ("Prices are recorded from
+  each refresh — check back in a few days"). No widget in v1 (one-kind rule).
+  Depends on the P0 archive.
 
 ## P2 — Later
 
@@ -69,6 +89,9 @@ Status: TODO / IN PROGRESS / DONE / BLOCKED.
 - [ ] **Localization** — UK English only today; audit string catalog for l10n.
 - [ ] **Dark mode polish** — verify brand logos (white-circle clips) and RAG dot
   contrast under dark appearance on-device.
+- [ ] **Trends: national average overlay + per-day min/max** — the full dump is
+  already held, so the UK/regional average line is computable locally; archive can
+  store per-day min/max so the chart shows intraday spikes, not just the daily point.
 
 ## P3 — Ideas / Research
 
@@ -84,8 +107,13 @@ Status: TODO / IN PROGRESS / DONE / BLOCKED.
   Public repo required for App Review (reviewer must fetch the data themselves);
   HTTPS/ATS fine; plain JSON data is not "remote code" (2.5.2-safe); bundle a small
   fallback dump so the app never demos empty. Needs GitHub PAT (aptonline account).
-- [ ] **Fuel-price prediction** — trend from historical dumps (relay could keep a
+- [ ] **Fuel-price prediction** — "price tends up/down" arrow derived from the
-  rolling archive) to show "price tends up/down".
+  price-history archive (P0). Cheap once the archive + Trends graph exist; keep a
+  separate phase. Backlog ancestry: this was the original "relay could keep a
+  rolling archive" idea — the archive is now P0 and the Trends graph (P1) is its
+  visible half.
+- [ ] **Widget sparkline** — medium-widget mini sparkline of a favourite's 30-day
+  trend, after the Trends UI lands (one-kind rule preserved).
 - [ ] **Price alerts for a specific station** — notify when a starred station's
   price drops below a user threshold.
 - [ ] **Share sheet** — share "Cheapest Unleaded near me" as text/image card.