Add Smart data checking mode

Shared/FuelStore.swift

@@ -370,6 +370,8 @@ struct FuelStore {
     static let liveActivityRadiusKey = "fuelboard.liveActivityRadiusMiles" // Int miles (5/10/15)
     static let onboardingCompletedKey = "fuelboard.onboardingCompleted" // Bool
     static let lastRefreshKey = "fuelboard.lastRefresh"      // TimeInterval (seconds since 1970)
+    static let dataRefreshModeKey = "fuelboard.dataRefreshMode" // DataRefreshMode raw value
+    static let lastSmartProbeKey = "fuelboard.lastSmartProbe" // TimeInterval (seconds since 1970)
     static let relaySourceKey = "fuelboard.relaySource"      // String — "api" | "csv"
     static let stationCountKey = "fuelboard.stationCount"    // String — station count
     static let dataUpdatedKey = "fuelboard.dataUpdated"      // String — govUK dataset update time
@@ -861,10 +863,24 @@ struct FuelStore {
         saveString(enabled ? "1" : "0", service: liveActivityFollowSearchKey)
     }
 
-    // MARK: Refresh policy — data is cached; the app only auto-refreshes
-    // twice a day (pull-to-refresh is the manual override).
+    // MARK: Refresh policy — Standard is cache-first/twice-daily; Smart keeps
+    // the same full-dump freshness cap but may probe the tiny mirror pointer
+    // more often in the background and only refresh the full dump if it changed.
 
     static let refreshInterval: TimeInterval = 12 * 60 * 60
+    static let smartProbeInterval: TimeInterval = 4 * 60 * 60
+
+    static func loadDataRefreshMode() -> DataRefreshMode {
+        if let raw = loadString(service: dataRefreshModeKey),
+           let mode = DataRefreshMode(rawValue: raw) {
+            return mode
+        }
+        return .standard
+    }
+
+    static func saveDataRefreshMode(_ mode: DataRefreshMode) {
+        saveString(mode.rawValue, service: dataRefreshModeKey)
+    }
 
     static func loadLastRefresh() -> Date? {
         if let raw = loadString(service: lastRefreshKey), let ts = TimeInterval(raw) {
@@ -877,6 +893,17 @@ struct FuelStore {
         saveString(String(date.timeIntervalSince1970), service: lastRefreshKey)
     }
 
+    static func loadLastSmartProbe() -> Date? {
+        if let raw = loadString(service: lastSmartProbeKey), let ts = TimeInterval(raw) {
+            return Date(timeIntervalSince1970: ts)
+        }
+        return nil
+    }
+
+    static func saveLastSmartProbe(_ date: Date = Date()) {
+        saveString(String(date.timeIntervalSince1970), service: lastSmartProbeKey)
+    }
+
     // MARK: Relay metadata — shown in Settings → About. Written after each
     // successful full fetch so the About section reflects the live source.
 
@@ -929,8 +956,17 @@ struct FuelStore {
     /// True when the cached data is fresh enough that a scheduled auto-refresh
     /// should be skipped (twice-a-day policy).
     static var isCacheFresh: Bool {
+        isCacheFresh(now: Date())
+    }
+
+    static func isCacheFresh(now: Date) -> Bool {
         guard let last = loadLastRefresh() else { return false }
-        return Date().timeIntervalSince(last) < refreshInterval
+        return now.timeIntervalSince(last) < refreshInterval
+    }
+
+    static func isSmartProbeDue(now: Date = Date()) -> Bool {
+        guard let last = loadLastSmartProbe() else { return true }
+        return now.timeIntervalSince(last) >= smartProbeInterval
     }
 
     // MARK: Onboarding — the app shows the intro screen on first launch only