App-side defensive price guard: drop grades outside 50-500p at decode (belt-and-braces vs relay regression)

Shared/FuelPriceProvider.swift

@@ -84,11 +84,15 @@ private struct RelayResponse: Codable {
         let prices: [String: Double]?
 
         /// Map relay grade keys (E5/E10/DIESEL) to FuelType for ALL fuels the
-        /// station sells — one fetch populates every fuel tab.
+        /// station sells — one fetch populates every fuel tab. Defensive guard:
+        /// any grade outside the 50–500 pence/litre band is dropped, so a relay
+        /// regression (e.g. the band being removed server-side) can't re-poison
+        /// the nationwide cheapest reference with 1.3p / 1589p garbage.
         var allPrices: [FuelType: Double] {
             var result: [FuelType: Double] = [:]
             if let prices {
                 for (grade, value) in prices {
+                    guard (50...500).contains(value) else { continue }
                     switch grade.uppercased() {
                     case "E10": result[.e10] = value
                     case "E5": result[.e5] = value
@@ -98,7 +102,7 @@ private struct RelayResponse: Codable {
                 }
             }
             // Backwards-compat: relay versions without `prices` still send `price`.
-            if result.isEmpty, let price {
+            if result.isEmpty, let price, (50...500).contains(price) {
                 result[.e10] = price
             }
             return result