feat: persist travel snapshots and refresh extended availability

src/Service/BookingService.php

@@ -112,7 +112,7 @@ class BookingService
      * Retrieves the booking DTO from the session and restores the Travel object.
      *
      * After deserialization the DTO contains only a Travel skeleton with the ID.
-     * This method replaces it with the full Travel from cache via hydrate().
+     * This method replaces it with the full Travel via hydrate().
      *
      * @param Request $request The HTTP request containing session data
      * @param string  $mode    The booking mode (create/edit)
@@ -159,11 +159,11 @@ class BookingService
     }
 
     /**
-     * Restores the full Travel object from cache after session deserialization.
+     * Restores the full Travel object after session deserialization.
      *
      * BookingDto::__serialize() replaces Travel with just its ID to keep session
-     * payloads small. This method fetches the complete Travel from the
-     * TravelDataService cache and sets it on both the DTO and the Booking reference.
+     * payloads small. This method fetches the complete Travel (from DB snapshot or
+     * XML fallback) and sets it on both the DTO and the Booking reference.
      */
     private function hydrate(BookingDto $bookingDto): void
     {