fix: backward compatibility for new session format

src/Form/Model/BookingDto.php

@@ -377,10 +377,15 @@ class BookingDto
             $this->$key = $value;
         }
 
-        // Create a skeleton Travel with only the ID; BookingService::hydrate()
-        // replaces this with the full object from cache
-        $travel = new Travel();
-        $travel->id = $travelId;
-        $this->travel = $travel;
+        // Old sessions (before c373a989) still carry a full Travel object;
+        // new sessions carry only the int ID. Handle both formats.
+        // TODO: Remove Travel instance branch once all pre-deploy sessions have expired
+        if ($travelId instanceof Travel) {
+            $this->travel = $travelId;
+        } else {
+            $travel = new Travel();
+            $travel->id = $travelId;
+            $this->travel = $travel;
+        }
     }
 }

tests/Form/Model/BookingDtoTest.php

@@ -28,4 +28,39 @@ class BookingDtoTest extends TestCase
         $this->assertSame($travel, $bookingDto->travel);
         $this->assertSame(BookingDto::MODE_CREATE, $bookingDto->getMode());
     }
+
+    public function testUnserializeHandlesIntTravelId(): void
+    {
+        $travel = new Travel();
+        $travel->id = 42;
+        $travel->dateFrom = new \DateTimeImmutable('2025-06-01');
+        $travel->dateTo = new \DateTimeImmutable('2025-06-08');
+
+        $dto = new BookingDto($travel, 1);
+        $serialized = serialize($dto);
+        $restored = unserialize($serialized);
+
+        $this->assertInstanceOf(BookingDto::class, $restored);
+        $this->assertSame(42, $restored->travel->id);
+    }
+
+    public function testUnserializeHandlesLegacyTravelObject(): void
+    {
+        $travel = new Travel();
+        $travel->id = 42;
+        $travel->dateFrom = new \DateTimeImmutable('2025-06-01');
+        $travel->dateTo = new \DateTimeImmutable('2025-06-08');
+
+        // Simulate old session format where 'travel' is a full Travel object
+        $data = [
+            'travel' => $travel,
+            'hotelId' => 1,
+        ];
+
+        $dto = new BookingDto(new Travel(), 1);
+        $dto->__unserialize($data);
+
+        $this->assertSame($travel, $dto->travel);
+        $this->assertSame(42, $dto->travel->id);
+    }
 }