P1: Favourites Trends graph — FuelHistoryStore + TrendsView (Swift Charts)

- Shared/FuelHistory.swift: GitHub mirror read path (latest.json pointer +
  history/YYYY-MM-DD.json day files); day math (UTC noon keys), slim day decode
  with the shared price band, series + deltaSeries (vs-cheapest rebase),
  favourites-only app-group cache (90-day prune), parallel per-day fetches,
  404/network = graph gap never error.
- FuelPriceProvider: shared priceBand + mapGrades (single source for live +
  history decoding).
- FuelBoard/TrendsView.swift: line chart in the Favourites tab via toolbar
  button + sheet; fuel capsule (fuels with favourites only), 7/30/90 range,
  Price/vs-cheapest toggle, per-station legend, price-display style on y-axis,
  empty/loading/retry states with honest copy; no widget in v1.
- Localizable.strings: Trends keys.
- 83 tests (13 history + URL regression): day math, band guard, series gaps,
  delta rebasing, prune, and the appendingPathComponent regression (relative
  URL resolution dropped /main — all fetches 404'd).
- Sim-verified: favourites rows + TOP/deltas; sheet controls + building-up
  state with live first-snapshot date (archive has 1 day; lines render once
  >=2 snapshots).
- Backlog: P1 Trends DONE (unmerged); P0 REMAINING = live provider chain +
  telemetry beacon.

BACKLOG.md

@@ -39,8 +39,10 @@ Status: TODO / IN PROGRESS / DONE / BLOCKED.
   (script ~/.hermes/scripts/mirror_push.py, log
   ~/Library/Logs/fuelboard-mirror.log); manual trigger `launchctl start
   com.apt.fuelboard-mirror`; first snapshot 2026-08-15 landed + verified raw 200.
-  REMAINING: app-side read (provider chain GitHub → relay → bundled dump) + the
-  telemetry beacon.*
+  REMAINING: live provider chain (GitHub → relay → bundled dump for CURRENT
+  prices) + the telemetry beacon — NOTE: the HISTORY read path shipped with P1
+  (FuelHistoryStore: latest.json + day files for starred stations, favourites-only
+  app-group cache, 404 = gap never error, 90-day prune).*
 
 ## P1 — Soon
 
@@ -56,7 +58,7 @@ 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.
+- [x] **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
@@ -64,7 +66,16 @@ Status: TODO / IN PROGRESS / DONE / BLOCKED.
   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.
+  Depends on the P0 archive. *DONE 2026-08-15 on feature/trends-history (unmerged):
+  `Shared/FuelHistory.swift` (FuelHistoryStore: day math, slim day decode w/ shared
+  band, series + deltaSeries, app-group favourites-only cache, parallel per-day
+  fetches) + `FuelBoard/TrendsView.swift` (chart, fuel capsule, 7/30/90, Price/vs
+  cheapest, per-station legend, empty/loading/retry states) + toolbar entry in
+  FavouritesView + strings. 83 tests incl. URL regression (appendingPathComponent
+  — URL(string:relativeTo:) dropped /main, all fetches 404'd). Sim-verified:
+  favourites rows + TOP/deltas; sheet controls + honest empty state w/ live first-
+  snapshot date. Pending: merge to main after device sideload test; lines render
+  once ≥2 snapshots (archive warming daily).*
 
 ## P2 — Later