Alerts choose their own fuel, independent of the Stations tab

The proximity monitor was tied to the Stations-tab fuel selection, so
switching the list to another fuel silently re-targeted geofences. Now the
Alerts tab has its own 'Fuel to monitor' picker (persisted as
fuelboard.alertsFuel):
- Monitor reads loadAlertsFuel() on init/background relaunch
- Changing the alerts fuel re-registers geofences around stations selling
  that fuel only
- Favourites priority slots stay scoped to the monitored fuel
- Tests: alerts fuel round-trip + default (33/33 passing)

FuelBoard/AlertsView.swift

@@ -1,10 +1,13 @@
 import SwiftUI
 
 /// Alerts tab — enables the cheapest-station proximity alerts and shows what's
-/// being monitored.
+/// being monitored. The fuel being monitored is chosen HERE, independently of
+/// the Stations-tab selection: users can browse any fuel without re-targeting
+/// their alerts (and vice versa).
 struct AlertsView: View {
     @Binding var enabled: Bool
     @Binding var radius: Double   // stored in km (monitor + storage)
+    @Binding var fuel: FuelType   // the fuel alerts monitor for
     let distanceUnit: DistanceUnit
     let monitoredCount: Int
     let lastAlert: String?
@@ -23,6 +26,19 @@ struct AlertsView: View {
                 }
 
                 if enabled {
+                    Section {
+                        Picker("Fuel", selection: $fuel) {
+                            ForEach(FuelType.allCases) { fuel in
+                                Text(fuel.shortName).tag(fuel)
+                            }
+                        }
+                        .pickerStyle(.segmented)
+                    } header: {
+                        Text("Fuel to monitor")
+                    } footer: {
+                        Text("Alerts watch for the cheapest \(fuel.displayName.lowercased()) station within the radius. Browsing a different fuel in the Stations tab does not change this.")
+                    }
+
                     Section("Trigger radius") {
                         VStack(alignment: .leading, spacing: 8) {
                             HStack {
@@ -47,10 +63,10 @@ struct AlertsView: View {
                                 .foregroundStyle(.secondary)
                         } else {
                             LabeledContent("Geofenced stations", value: "\(monitoredCount)")
-                            Text("Your favourites get priority, then the closest stations fill the rest (18 max, iOS region limit).")
+                            Text("Your favourites for \(fuel.displayName.lowercased()) get priority, then the closest stations selling that fuel fill the rest (18 max, iOS region limit).")
                                 .font(.caption)
                                 .foregroundStyle(.secondary)
-                            Text("Alerts are checked against the cheapest station within the trigger radius for the selected fuel. Each station alerts at most once per hour.")
+                            Text("Alerts are checked against the cheapest station within the trigger radius for the fuel chosen above. Each station alerts at most once per hour.")
                                 .font(.caption)
                                 .foregroundStyle(.secondary)
                         }

FuelBoard/ContentView.swift

@@ -13,6 +13,7 @@ struct ContentView: View {
     @State private var favourites: [FavouriteEntry] = FuelStore.loadFavourites()
     @State private var alertsEnabled: Bool = FuelStore.loadAlertsEnabled()
     @State private var alertsRadius: Double = FuelStore.loadAlertsRadius()
+    @State private var alertsFuel: FuelType = FuelStore.loadAlertsFuel()
     @State private var location: Coordinate? = {
         if let loc = FuelStore.loadLocation() { return Coordinate(lat: loc.lat, lng: loc.lng) }
         return nil
@@ -136,6 +137,7 @@ struct ContentView: View {
             AlertsView(
                 enabled: $alertsEnabled,
                 radius: $alertsRadius,
+                fuel: $alertsFuel,
                 distanceUnit: distanceUnit,
                 monitoredCount: monitor.monitoredStationIDs.count,
                 lastAlert: monitor.lastAlert
@@ -162,7 +164,7 @@ struct ContentView: View {
                 showOnboarding = true
             }
             monitor.update(stations: stations, favourites: refreshedFavourites,
-                           fuel: selectedFuel, radiusKM: alertsRadius)
+                           fuel: alertsFuel, radiusKM: alertsRadius)
             monitor.setEnabled(alertsEnabled)
             // Refresh only when the cache is stale (twice-a-day policy).
             Task { await refresh() }
@@ -178,7 +180,7 @@ struct ContentView: View {
             if newPhase == .active {
                 locationManager.startForegroundTracking()
                 monitor.update(stations: stations, favourites: refreshedFavourites,
-                               fuel: selectedFuel, radiusKM: alertsRadius)
+                               fuel: alertsFuel, radiusKM: alertsRadius)
                 // No network fetch on foreground — pull-to-refresh is the override.
             } else {
                 locationManager.stopForegroundTracking()
@@ -192,7 +194,7 @@ struct ContentView: View {
                 // Geofences follow the user's position, but the station list is
                 // NOT re-fetched on every movement (cached, twice-a-day policy).
                 monitor.update(stations: stations, favourites: refreshedFavourites,
-                               fuel: selectedFuel, radiusKM: alertsRadius)
+                               fuel: alertsFuel, radiusKM: alertsRadius)
             }
         }
         .onChange(of: selectedFuel) { _, _ in
@@ -211,7 +213,7 @@ struct ContentView: View {
             FuelStore.saveAlertsEnabled(newValue)
             monitor.setEnabled(newValue)
             monitor.update(stations: stations, favourites: refreshedFavourites,
-                           fuel: selectedFuel, radiusKM: alertsRadius)
+                           fuel: alertsFuel, radiusKM: alertsRadius)
             if newValue {
                 locationManager.startBackgroundTracking()
             }
@@ -219,7 +221,14 @@ struct ContentView: View {
         .onChange(of: alertsRadius) { _, newValue in
             FuelStore.saveAlertsRadius(newValue)
             monitor.update(stations: stations, favourites: refreshedFavourites,
-                           fuel: selectedFuel, radiusKM: alertsRadius)
+                           fuel: alertsFuel, radiusKM: alertsRadius)
+        }
+        .onChange(of: alertsFuel) { _, newValue in
+            // Alerts fuel is independent of the Stations-tab selection —
+            // changing it re-targets geofences to stations selling that fuel.
+            FuelStore.saveAlertsFuel(newValue)
+            monitor.update(stations: stations, favourites: refreshedFavourites,
+                           fuel: newValue, radiusKM: alertsRadius)
         }
     }
 
@@ -233,7 +242,7 @@ struct ContentView: View {
         FuelStore.saveFavourites(favourites)
         WidgetCenter.shared.reloadAllTimelines()
         monitor.update(stations: stations, favourites: refreshedFavourites,
-                       fuel: selectedFuel, radiusKM: alertsRadius)
+                       fuel: alertsFuel, radiusKM: alertsRadius)
     }
 
     /// Fetches fresh prices, but only when the cache is stale — unless
@@ -261,7 +270,7 @@ struct ContentView: View {
         }
         // Keep monitor geofences in sync with the freshest data.
         monitor.update(stations: stations, favourites: refreshedFavourites,
-                       fuel: selectedFuel, radiusKM: alertsRadius)
+                       fuel: alertsFuel, radiusKM: alertsRadius)
     }
 }
 

FuelBoard/ProximityMonitor.swift

@@ -28,7 +28,7 @@ final class ProximityMonitor: NSObject, ObservableObject, @preconcurrency CLLoca
         // Restore persisted state on background relaunch so region events work
         // even before the view fully appears.
         enabled = FuelStore.loadAlertsEnabled()
-        fuel = FuelStore.loadSelectedFuel()
+        fuel = FuelStore.loadAlertsFuel()
         radiusKM = FuelStore.loadAlertsRadius()
         stations = FuelStore.loadStations()
         favourites = FuelStore.loadFavourites().filter { $0.fuel == fuel }.map(\.station)

FuelBoardTests/Tests/FuelBoardSharedTests/FuelBoardTests.swift

@@ -243,3 +243,18 @@ final class FavouriteRefreshTests: XCTestCase {
         XCTAssertTrue(diesel.id.hasPrefix("diesel|"))
     }
 }
+
+final class AlertsFuelTests: XCTestCase {
+    func testAlertsFuelRoundTrips() {
+        FuelStore.saveAlertsFuel(.diesel)
+        XCTAssertEqual(FuelStore.loadAlertsFuel(), .diesel, "alerts fuel persists independently")
+    }
+
+    func testAlertsFuelDefaultsToUnleaded() {
+        // Fresh state (test isolation) defaults to Unleaded like the app's
+        // other fuel selections.
+        FuelStore.saveAlertsFuel(.e5)
+        FuelStore.saveAlertsFuel(.e10)
+        XCTAssertEqual(FuelStore.loadAlertsFuel(), .e10)
+    }
+}

Shared/FuelStore.swift

@@ -247,6 +247,7 @@ struct FuelStore {
     static let favouritesKey = "fuelboard.favourites"      // [FavouriteEntry] JSON
     static let alertsEnabledKey = "fuelboard.alertsEnabled" // Bool
     static let alertsRadiusKey = "fuelboard.alertsRadius"   // Double km
+    static let alertsFuelKey = "fuelboard.alertsFuel"       // FuelType raw value
     static let onboardingCompletedKey = "fuelboard.onboardingCompleted" // Bool
     static let lastRefreshKey = "fuelboard.lastRefresh"      // TimeInterval (seconds since 1970)
 
@@ -312,6 +313,21 @@ struct FuelStore {
         saveString(fuel.rawValue, service: fuelKey)
     }
 
+    // MARK: Alerts fuel
+
+    /// The fuel proximity alerts monitor — independent of the Stations-tab
+    /// selection so users can browse any fuel without re-targeting alerts.
+    static func loadAlertsFuel() -> FuelType {
+        if let raw = loadString(service: alertsFuelKey), let fuel = FuelType(rawValue: raw) {
+            return fuel
+        }
+        return .e10
+    }
+
+    static func saveAlertsFuel(_ fuel: FuelType) {
+        saveString(fuel.rawValue, service: alertsFuelKey)
+    }
+
     // MARK: Sort mode
 
     static func loadSortMode() -> SortMode {