Backlog: P0 archive reshaped to GitHub price-history mirror (relay pushes daily latest.json + history/YYYY-MM-DD.json to public fuelboard-data repo; app reads raw.githubusercontent); P3 production-mirror item absorbed into P0

BACKLOG.md

@@ -11,14 +11,25 @@ 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`).
+- [ ] **GitHub price-history mirror (start now — warm the data for Trends)** — the
+  relay does the GOV.UK heavy lifting (OAuth token stays in relay `.env`) and
+  pushes a daily snapshot to a PUBLIC repo; the app reads from GitHub, so this
+  doubles as the production data source (App Review can't reach the LAN relay) AND
+  the history archive the Trends graph (P1) reads. Shape: relay writes
+  `latest.json` (tiny pointer: date, station_count, data_updated, available range)
+  + `history/YYYY-MM-DD.json` (full ~200 KB dump) and pushes once/day; the app
+  fetches `raw.githubusercontent.com/aptonline/fuelboard-data/main/latest.json`,
+  then only the missing day files for starred (station, fuel) pairs (deterministic
+  URLs — 404 = no data that day, leave a graph gap, never error). LAN relay stays
+  the fallback source. Setup: create the PUBLIC repo `aptonline/fuelboard-data`
+  (gh installed); GitHub PAT (aptonline) lives in relay `.env` only — never in the
+  repo or IPA. App Review: public repo required (reviewer fetches the data
+  themselves); HTTPS/ATS fine; plain JSON is not "remote code" (2.5.2-safe); bundle
+  a small fallback dump so the app never demos empty. Growth ~200 KB/day (~73 MB/yr
+  — no pruning for years); git history doubles as an audit trail. Optional
+  first-weeks tweak: hourly pushes to build history faster, then settle to daily.
+  Accumulating TODAY means the Trends graph launches with weeks of real history
+  instead of an empty chart.
 
 ## P1 — Soon
 
@@ -101,12 +112,6 @@ Status: TODO / IN PROGRESS / DONE / BLOCKED.
 - [ ] **App Intents testing** — AppIntentsTesting (iOS 27) for intent coverage
   instead of XCUITest when the Siri features land.
 
-- [ ] **Production data mirror (GitHub)** — relay pushes the synced dump
-  (`stations.json` + `latest.json` version pointer) to a PUBLIC GitHub repo; the
-  app fetches `raw.githubusercontent.com` with the LAN relay as fallback source.
-  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** — "price tends up/down" arrow derived from the
   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