Add Worth the Drive fuel savings with road-routed estimates

Optional Fuel Savings feature (off by default): vehicle MPG in UK imperial gallons, fill amount in pounds or litres, persisted through the existing keychain/app-group store. Ranks the WHOLE station pool by estimated net saving (fuel-price saving at each pump minus the extra return-trip driving cost) using MapKit road distances with a straight-line fallback marked (est.).

The closest station with a valid price for the selected fuel is the comparison baseline and is labelled "Closest station"; other rows read "Save £X.XX after travel" / "£X.XX worse off after travel" / "Break even". Labels live in the shared model so they are unit-tested. The TOP badge still marks the cheapest pump price and reads "CHEAPEST" when the list is ranked by net saving.

Road routing now prioritises the Worth-the-Drive candidates plus the baseline and merges cache entries instead of replacing them, so far-out stations get real routes rather than permanent straight-line estimates. Numeric fields gain a Done button above the keypad (decimalPad has no Return key); the fill-up control is hidden unless the feature is configured; Favourites shares one session fill amount with the station list. 131 tests.

FuelBoard/StationsView.swift

@@ -16,6 +16,10 @@ struct StationsView: View {
     let location: Coordinate?
     let favouriteIDs: Set<String>
     let stationTapAction: StationTapAction
+    let fuelSavingsSettings: FuelSavingsSettings
+    @Binding var fuelSavingsAmount: FuelSavingsFillAmount
+    var savingsForStation: (FuelStation) -> FuelSavingsAvailability? = { _ in nil }
+    var savingsBaselineStationName: String?
     var onToggleFavourite: (FuelStation, FuelType) -> Void = { _, _ in }
     var onRefresh: () async -> Void = {}
 
@@ -41,7 +45,12 @@ struct StationsView: View {
         let miles = distanceUnit.displayMiles(stationLimit)
         let unit = distanceUnit.label(for: Double(miles))
         let fuel = selectedFuel.displayName
-        let mode = sortMode == .closest ? "Closest" : "Cheapest"
+        let mode: String
+        switch sortMode {
+        case .closest: mode = "Closest"
+        case .cheapest: mode = "Cheapest"
+        case .worthTheDrive: mode = "Worth the Drive"
+        }
         let tapHint = stationTapAction == .openMap
             ? "tap a station for directions."
             : "tap a station for details."
@@ -92,7 +101,7 @@ struct StationsView: View {
 
                 Section("Stations") {
                     Picker("Sort by", selection: $sortMode) {
-                        ForEach(SortMode.allCases) { mode in
+                        ForEach(availableSortModes) { mode in
                             Text(mode.displayName).tag(mode)
                         }
                     }
@@ -102,7 +111,17 @@ struct StationsView: View {
                     }
                     .padding(.vertical, 2)
 
-                    if isLoading {
+                    // Only offered while the feature is actually configured — a
+                    // stale stored sort mode must not keep the control on screen
+                    // for a switched-off feature.
+                    if sortMode == .worthTheDrive && fuelSavingsSettings.isConfigured {
+                        FuelSavingsAdjustmentView(
+                            amount: $fuelSavingsAmount,
+                            referencePricePencePerLitre: baselinePrice
+                        )
+                    }
+
+                    if isLoading && stations.isEmpty {
                         HStack(spacing: 10) {
                             ProgressView()
                             Text("Fetching prices…")
@@ -133,7 +152,9 @@ struct StationsView: View {
                                 baselinePrice: baselinePrice,
                                 isTopResult: station.id == topStationID,
                                 isFavourite: favouriteIDs.contains(station.id),
+                                topBadgeText: sortMode == .worthTheDrive ? "CHEAPEST" : "TOP",
                                 tapAction: stationTapAction,
+                                fuelSavings: savingsForStation(station),
                                 onToggleFavourite: { onToggleFavourite(station, selectedFuel) },
                                 onShowDetails: { detailStation = $0 }
                             )
@@ -180,6 +201,11 @@ struct StationsView: View {
             // large title at rest, scrolls it away and fades the compact
             // inline title in. No custom toolbar needed — the native mechanism
             // only renders text, which is exactly what we want here.
+            // The Worth the Drive fill-up box uses `.decimalPad`, which has no
+            // Return key — give the keyboard a Done button and let a scroll
+            // dismiss it too.
+            .keyboardDoneButton()
+            .scrollDismissesKeyboard(.interactively)
             .navigationTitle("FuelBoard")
             .navigationBarTitleDisplayMode(.large)
             .onAppear {
@@ -273,12 +299,23 @@ struct StationsView: View {
                 StationDetailView(
                     station: station,
                     location: location,
-                    distanceUnit: distanceUnit
+                    distanceUnit: distanceUnit,
+                    fuelSavings: savingsForStation(station),
+                    fuelSavingsAmount: fuelSavingsAmount,
+                    savingsBaselineStationName: savingsBaselineStationName
                 )
             }
         }
     }
 
+    private var availableSortModes: [SortMode] {
+        var modes: [SortMode] = [.closest, .cheapest]
+        if fuelSavingsSettings.isConfigured {
+            modes.append(.worthTheDrive)
+        }
+        return modes
+    }
+
     /// One price-rating card for the Key sheet: accent icon, title + blurb,
     /// and the rating threshold in the accent colour (mirrors the tip cards).
     private func keyCard(icon: String, color: Color, title: String, blurb: String, threshold: String) -> some View {