feat: report the source export timestamp on every travel export page

src/Controller/Api/ExportController.php

@@ -59,6 +59,7 @@ class ExportController extends AbstractController
                 'totalPages' => (int) ceil($total / $query->perPage),
                 'skipped' => $export->skipped,
                 'pickupsWithoutMasterData' => $export->pickupsWithoutMasterData,
+                'sourceGeneratedAt' => $export->sourceGeneratedAt?->format('c'),
                 'generatedAt' => $export->generatedAt->format('c'),
             ],
         ]);

src/Model/TravelExport.php

@@ -19,12 +19,14 @@ final readonly class TravelExport
      * @param list<array<string, mixed>> $rows                     one row per (travel, hotel) pair
      * @param int                        $skipped                  (travel, hotel) pairs dropped as unusable
      * @param int                        $pickupsWithoutMasterData distinct pickup ids absent from zustiege.xml
+     * @param \DateTimeImmutable|null    $sourceGeneratedAt        the uebertragung.info timestamp of the export read, null if unknown
      */
     public function __construct(
         public array $rows,
         public int $skipped,
         public int $pickupsWithoutMasterData,
         public \DateTimeImmutable $generatedAt,
+        public ?\DateTimeImmutable $sourceGeneratedAt = null,
     ) {
     }
 }

src/Service/TravelExportBuilder.php

@@ -6,6 +6,7 @@ namespace App\Service;
 
 use App\BusProNet\Model\Hotel;
 use App\BusProNet\Model\Pickup;
+use App\BusProNet\Model\XmlExportInfo;
 use App\BusProNet\Traits\TypeConversionTrait;
 use App\BusProNet\XmlCrawlerFactory;
 use App\BusProNet\XmlLoader\HotelLoader;
@@ -67,6 +68,11 @@ class TravelExportBuilder
 
     private function assemble(): TravelExport
     {
+        // Read before the walk and cached with the rows, so every page served from this
+        // copy names the same source export. A client that sees it change between pages
+        // knows xml-sync swapped the export underneath its walk.
+        $sourceGeneratedAt = XmlExportInfo::fromStorage($this->xmlExport)?->lastTransfer;
+
         $hotels = $this->hotelLoader->loadAll();
         $pickupMasterData = $this->pickupLoader->loadAll();
 
@@ -96,6 +102,7 @@ class TravelExportBuilder
             $skipped,
             count($pickupsWithoutMasterData),
             new \DateTimeImmutable(),
+            $sourceGeneratedAt,
         );
     }