road distance: cover all in-radius stations, not just nearest 12

Stations past the nearest-12 cutoff silently fell back to straight-line,
which explained the remaining app-vs-Apple-Maps gaps (e.g. 3.5 straight-line
vs 5.9 road). Raise the per-pass cap to 40 and route every station within a
25 km straight-line radius (covers the 15 mi max search window) so any station
the widget/Live Activity/list can show gets a real road distance.

Also harden the new cache tests against persistent keychain state across
invocations (reset in setUp) so they pass deterministically.

FuelBoard/ContentView.swift

@@ -50,6 +50,21 @@ struct ContentView: View {
             // fires on every fix incl. background significant-change
             // wake-ups, so the Lock Screen pill stays live while driving.
             updateLiveActivity()
+            refreshRoadDistancesIfNeeded()
+        }
+    }
+
+    /// Kicks off a (throttled) Apple-Maps road-distance recompute for the
+    /// stations around the current fix. The app owns routing — the widget and
+    /// Live Activity only read the cached result.
+    private func refreshRoadDistancesIfNeeded() {
+        guard let location else { return }
+        Task {
+            await RoadDistanceService.refreshIfNeeded(
+                stations: stations,
+                lat: location.lat,
+                lng: location.lng
+            )
         }
     }
 
@@ -377,6 +392,7 @@ struct ContentView: View {
                 monitor.update(stations: stations, favourites: refreshedFavourites,
                                fuel: alertsFuel, radiusKM: effectiveAlertsRadiusKM)
                 updateLiveActivity()
+                refreshRoadDistancesIfNeeded()
             }
         }
         )
@@ -949,7 +965,7 @@ struct StationRow: View {
                     .lineLimit(1)
                     .truncationMode(.tail)
                 if let location {
-                    Text(distanceUnit.format(station.distanceKM(to: location.lat, lng2: location.lng)))
+                    Text(distanceUnit.format(FuelStore.displayDistanceKM(station: station, userLat: location.lat, userLng: location.lng)))
                         .font(.caption2)
                         .foregroundStyle(.secondary)
                         .monospacedDigit()

FuelBoard/LiveActivityManager.swift

@@ -57,7 +57,7 @@ enum LiveActivityManager {
             brand: best.brand,
             pricePence: price,
             priceDisplayStyle: priceDisplayStyle ?? FuelStore.loadPriceDisplayStyle(),
-            distanceKM: best.distanceKM(to: location.lat, lng2: location.lng),
+            distanceKM: FuelStore.displayDistanceKM(station: best, userLat: location.lat, userLng: location.lng),
             lat: best.lat,
             lng: best.lng,
             updatedAt: Date()

FuelBoard/RoadDistanceService.swift

@@ -0,0 +1,93 @@
+// RoadDistanceService.swift — computes Apple-Maps-matched ROAD distances for
+// nearby stations and caches them (keychain) so widgets + Live Activity can
+// show real driving distance instead of straight-line haversine.
+//
+// Runs only in the APP: MKDirections is network-bound and the widget extension
+// has a tiny execution budget + a ~40-70/day refresh budget, so routing belongs
+// here, not in the widget. The widget/Live Activity just read the cache.
+//
+// Throttling: recompute at most every `throttleMinutes`, or when the user has
+// moved `moveThresholdMeters` from where the cache was built. Bounded to the
+// `candidatesPerPass` nearest stations so a pass stays a handful of route calls.
+
+import Foundation
+import MapKit
+import WidgetKit
+
+enum RoadDistanceService {
+    /// Upper bound on stations routed per pass, so a pass stays a bounded set of
+    /// route calls. Raised from 12 so stations past the old nearest-12 cutoff
+    /// still get real road distances instead of a straight-line fallback.
+    static let candidatesPerPass = 40
+    /// Only route stations within this straight-line radius (km). Covers the
+    /// largest search radius the UI exposes (15 mi ≈ 24.1 km) plus margin, so
+    /// every station a widget/Live Activity/list can actually show gets routed.
+    static let maxRadiusKM: Double = 25
+    /// Don't route again more often than this (minutes).
+    static let throttleMinutes: Double = 10
+    /// Recompute when the user moves more than this (metres) from the last
+    /// source location.
+    static let moveThresholdMeters: Double = 400
+
+    /// Refreshes the cached road distances for the in-radius stations around
+    /// `lat`/`lng`. Throttled by time + distance; safe to call on every fix.
+    static func refreshIfNeeded(stations: [FuelStation], lat: Double, lng: Double) async {
+        guard !stations.isEmpty else { return }
+
+        // Throttle: keep cached values when fresh and the user hasn't moved far.
+        if let cache = FuelStore.loadRoadDistances() {
+            let elapsed = Date().timeIntervalSince1970 - cache.updatedAt
+            let movedMeters = haversineMeters(cache.sourceLat, cache.sourceLng, lat, lng)
+            if elapsed < throttleMinutes * 60 && movedMeters < moveThresholdMeters {
+                return
+            }
+        }
+
+        // Candidate stations: the nearest-by-straight-line subset that the UI
+        // could actually display, capped so a pass stays bounded.
+        let nearest = stations
+            .sorted { $0.distanceKM(to: lat, lng2: lng) < $1.distanceKM(to: lat, lng2: lng) }
+            .prefix(candidatesPerPass)
+            .filter { $0.distanceKM(to: lat, lng2: lng) <= maxRadiusKM }
+
+        let origin = CLLocationCoordinate2D(latitude: lat, longitude: lng)
+        var entries: [String: Double] = [:]
+        for station in nearest {
+            let dest = CLLocationCoordinate2D(latitude: station.lat, longitude: station.lng)
+            if let meters = await roadMeters(from: origin, to: dest) {
+                entries[station.id] = meters
+            }
+        }
+        guard !entries.isEmpty else { return }
+
+        FuelStore.saveRoadDistances(sourceLat: lat, sourceLng: lng, entries: entries)
+        // Wake the widgets so the new road distances surface immediately.
+        WidgetCenter.shared.reloadAllTimelines()
+    }
+
+    /// Driving distance (metres) between two coordinates via Apple Maps routing.
+    private static func roadMeters(from: CLLocationCoordinate2D, to: CLLocationCoordinate2D) async -> Double? {
+        let request = MKDirections.Request()
+        request.source = MKMapItem(placemark: MKPlacemark(coordinate: from))
+        request.destination = MKMapItem(placemark: MKPlacemark(coordinate: to))
+        request.transportType = .automobile
+        request.requestsAlternateRoutes = false
+        do {
+            let response = try await MKDirections(request: request).calculate()
+            return response.routes.first?.distance
+        } catch {
+            return nil
+        }
+    }
+
+    /// Straight-line haversine distance between two coordinates, in metres.
+    private static func haversineMeters(_ lat1: Double, _ lng1: Double, _ lat2: Double, _ lng2: Double) -> Double {
+        let r = 6371000.0
+        let dLat = (lat2 - lat1) * .pi / 180
+        let dLng = (lng2 - lng1) * .pi / 180
+        let a = sin(dLat / 2) * sin(dLat / 2) +
+                cos(lat1 * .pi / 180) * cos(lat2 * .pi / 180) *
+                sin(dLng / 2) * sin(dLng / 2)
+        return r * 2 * atan2(sqrt(a), sqrt(1 - a))
+    }
+}

FuelBoardTests/Tests/FuelBoardSharedTests/FuelBoardTests.swift

@@ -620,3 +620,54 @@ final class OfflineDataLabelTests: XCTestCase {
         XCTAssertNil(FuelStore.offlineDataLabel(from: "not-a-date"))
     }
 }
+
+// MARK: - Road distance cache
+
+final class RoadDistanceCacheTests: XCTestCase {
+    override func setUp() {
+        super.setUp()
+        // Keychain persists across invocations, so a cache left by an earlier
+        // test or run would pollute these. Overwrite with an empty, far-away
+        // cache (source at (0,0)) so every test starts from a clean slate.
+        FuelStore.saveRoadDistances(sourceLat: 0, sourceLng: 0, entries: [:])
+    }
+
+    private func station(_ id: String, _ lat: Double, _ lng: Double) -> FuelStation {
+        FuelStation(id: id, name: id, brand: "X", address: "", postcode: "",
+                    lat: lat, lng: lng, prices: [:], priceUpdated: nil)
+    }
+
+    func testDisplayDistanceFallsBackToStraightLineWhenNoCache() {
+        // London user, station ~ London -> no cache -> straight-line haversine.
+        let s = station("a", 51.5074, -0.1278)
+        let km = FuelStore.displayDistanceKM(station: s, userLat: 51.6, userLng: -0.1)
+        XCTAssertEqual(km, s.distanceKM(to: 51.6, lng2: -0.1), accuracy: 0.0001)
+    }
+
+    func testRoadDistanceUsedWhenCachedNear() {
+        let s = station("a", 51.5074, -0.1278)
+        // Cache a road distance of 3.2 km for this station from the user's fix.
+        FuelStore.saveRoadDistances(sourceLat: 51.6, sourceLng: -0.1, entries: ["a": 3200])
+        let km = FuelStore.displayDistanceKM(station: s, userLat: 51.6, userLng: -0.1)
+        XCTAssertEqual(km, 3.2, accuracy: 0.0001)
+    }
+
+    func testRoadDistanceNilWhenOriginFar() {
+        let s = station("a", 51.5074, -0.1278)
+        // Cache built in London, but the user is now ~200 km away -> stale.
+        FuelStore.saveRoadDistances(sourceLat: 51.5074, sourceLng: -0.1278, entries: ["a": 3200])
+        let meters = FuelStore.roadDistanceMeters(for: "a", userLat: 53.4808, userLng: -2.2426)
+        XCTAssertNil(meters)
+        // And display falls back to straight-line.
+        let km = FuelStore.displayDistanceKM(station: s, userLat: 53.4808, userLng: -2.2426)
+        XCTAssertEqual(km, s.distanceKM(to: 53.4808, lng2: -2.2426), accuracy: 0.0001)
+    }
+
+    func testRoadDistanceUsedForOtherStationNotFound() {
+        FuelStore.saveRoadDistances(sourceLat: 51.6, sourceLng: -0.1, entries: ["a": 3200])
+        // A station that isn't in the cache falls back to straight-line.
+        let s = station("z", 51.51, -0.13)
+        let km = FuelStore.displayDistanceKM(station: s, userLat: 51.6, userLng: -0.1)
+        XCTAssertEqual(km, s.distanceKM(to: 51.6, lng2: -0.1), accuracy: 0.0001)
+    }
+}

Shared/FuelPriceWidgetViews.swift

@@ -89,7 +89,7 @@ struct FuelPriceWidgetContent: View {
                 FuelStore.priceTextAttributed(price, size: 26, weight: .bold, color: .green)
             }
             if let location = entry.location {
-                Text(entry.unit.format(station.distanceKM(to: location.lat, lng2: location.lng)) + " away")
+                Text(entry.unit.format(FuelStore.displayDistanceKM(station: station, userLat: location.lat, userLng: location.lng)) + " away")
                     .font(.caption2)
                     .foregroundStyle(.secondary)
             } else {
@@ -148,7 +148,7 @@ struct FuelPriceWidgetContent: View {
                 .font(.caption.weight(.semibold))
                 .lineLimit(1)
             if let location = entry.location {
-                Text(entry.unit.format(station.distanceKM(to: location.lat, lng2: location.lng)))
+                Text(entry.unit.format(FuelStore.displayDistanceKM(station: station, userLat: location.lat, userLng: location.lng)))
                     .font(.caption2)
                     .foregroundStyle(.secondary)
             }

Shared/FuelStore.swift

@@ -945,6 +945,62 @@ struct FuelStore {
         UserDefaults(suiteName: appGroupSuite)?.set(completed, forKey: onboardingCompletedKey)
     }
 
+    // MARK: Road distances (Apple-Maps-matched, computed by the app)
+
+    /// Cached road/routed distances (metres) keyed by station ID, computed by
+    /// the app via MapKit `MKDirections`. Stored in KEYCHAIN (survives on free
+    /// SideStore accounts where the app-group container isn't provisioned) so
+    /// the widget extension can read it too. Widget + Live Activity prefer
+    /// these over straight-line haversine for the displayed distance.
+    static let roadDistancesKey = "fuelboard.roadDistances"
+
+    /// How far (metres) the cache's source location may be from the current
+    /// user position before a cached road distance is treated as stale.
+    static let roadDistanceOriginToleranceMeters: Double = 600
+
+    static func saveRoadDistances(sourceLat: Double, sourceLng: Double, entries: [String: Double]) {
+        let cache = RoadDistanceCache(sourceLat: sourceLat, sourceLng: sourceLng,
+                                      updatedAt: Date().timeIntervalSince1970, entries: entries)
+        if let data = try? JSONEncoder().encode(cache) {
+            saveString(data.base64EncodedString(), service: roadDistancesKey)
+        }
+    }
+
+    static func loadRoadDistances() -> RoadDistanceCache? {
+        guard let raw = loadString(service: roadDistancesKey),
+              let data = Data(base64Encoded: raw),
+              let cache = try? JSONDecoder().decode(RoadDistanceCache.self, from: data)
+        else { return nil }
+        return cache
+    }
+
+    /// Cached road distance (metres) to a station from the user's location, or
+    /// nil when not cached / the cache was built too far from where the user
+    /// is now.
+    static func roadDistanceMeters(for stationID: String, userLat: Double, userLng: Double) -> Double? {
+        guard let cache = loadRoadDistances(),
+              let meters = cache.entries[stationID] else { return nil }
+        // The cache is only valid near the location it was built from.
+        let dLat = (userLat - cache.sourceLat) * .pi / 180
+        let dLng = (userLng - cache.sourceLng) * .pi / 180
+        let r = 6371000.0
+        let a = sin(dLat / 2) * sin(dLat / 2) +
+                cos(cache.sourceLat * .pi / 180) * cos(userLat * .pi / 180) *
+                sin(dLng / 2) * sin(dLng / 2)
+        let originDistanceMeters = r * 2 * atan2(sqrt(a), sqrt(1 - a))
+        guard originDistanceMeters <= roadDistanceOriginToleranceMeters else { return nil }
+        return meters
+    }
+
+    /// Distance (km) to display for a station: cached ROAD distance when
+    /// available (matches Apple Maps), else straight-line haversine.
+    static func displayDistanceKM(station: FuelStation, userLat: Double, userLng: Double) -> Double {
+        if let meters = roadDistanceMeters(for: station.id, userLat: userLat, userLng: userLng) {
+            return meters / 1000.0
+        }
+        return station.distanceKM(to: userLat, lng2: userLng)
+    }
+
     // MARK: Low-level keychain helpers
 
     private static func keychainData(service: String) -> Data? {
@@ -1004,3 +1060,12 @@ struct FuelStore {
         loadString(service: "widget.diag.\(intentType)")
     }
 }
+
+/// Cached Apple-Maps road distances for nearby stations (see
+/// `FuelStore.roadDistancesKey`). `entries` maps stationID → road metres.
+struct RoadDistanceCache: Codable {
+    let sourceLat: Double
+    let sourceLng: Double
+    let updatedAt: TimeInterval
+    let entries: [String: Double]
+}