fix: address code review findings

internal/cache/store.go

@@ -116,10 +116,16 @@ func keyString(k *CacheKey) string {
 	case k.Kind == "station":
 		return fmt.Sprintf("stations:%s", sanitizeKeyComponent(k.Code))
 	case k.Kind == "search":
-		return fmt.Sprintf("search:%s:%s:%s",
+		// Include far-term flag in cache key to distinguish near-term (3-hour TTL) from far-term (7-day TTL)
+		farTermFlag := "near"
+		if k.Request != "" {
+			farTermFlag = k.Request
+		}
+		return fmt.Sprintf("search:%s:%s:%s:%s",
 			sanitizeKeyComponent(k.From),
 			sanitizeKeyComponent(k.To),
-			sanitizeKeyComponent(k.Date))
+			sanitizeKeyComponent(k.Date),
+			farTermFlag)
 	default:
 		return fmt.Sprintf("unknown:%s", sanitizeKeyComponent(k.Kind))
 	}