Siri: scope cheapest-near-me to the saved search radius (5/10/15 mi)

Shared/SiriCheapestLookup.swift

@@ -5,17 +5,25 @@ import Foundation
 /// targets, and FuelBoardTests exercises this directly.
 enum SiriCheapestLookup {
 
-    /// The cheapest station selling `fuel`, tie-broken by distance from the
-    /// given point. Stations without a price for `fuel` are skipped entirely.
-    /// Returns nil when no station sells the fuel.
+    /// The cheapest station selling `fuel` WITHIN `withinMiles` of the given
+    /// point, tie-broken by distance. Stations without a price for `fuel`, or
+    /// farther than the radius, are skipped entirely. Returns nil when no
+    /// station sells the fuel inside the radius.
+    ///
+    /// Radius scoping mirrors the app's Stations tab (search radius
+    /// 5/10/15 mi): without it, "cheapest near me" silently answers the
+    /// UK-wide minimum — a genuinely cheap station hundreds of miles away
+    /// (found with real data: GULF HISTON 100.9p was 132 mi from the phone).
     static func cheapest(
         in stations: [FuelStation],
         fuel: FuelType,
         fromLat lat: Double,
-        lng: Double
+        lng: Double,
+        withinMiles: Double
     ) -> FuelStation? {
-        stations
-            .filter { $0.prices[fuel] != nil }
+        let radiusKM = withinMiles * 1.60934
+        return stations
+            .filter { $0.prices[fuel] != nil && $0.distanceKM(to: lat, lng2: lng) <= radiusKM }
             .min { lhs, rhs in
                 guard let lp = lhs.prices[fuel], let rp = rhs.prices[fuel] else {
                     return false