fix: reset room assignments after updated selection if required

src/Controller/Booking/Create/Step2Controller.php

@@ -74,6 +74,9 @@ class Step2Controller extends AbstractController
             fn ($user, $participant) => $this->prepopulationService->prepopulateApplicantFromUser($user, $participant)
         );
 
+        // Validate room assignments against current selection (handles back-navigation from step 2 to step 1)
+        $this->roomAssignmentService->validateAndResetInvalidAssignments($bookingCreateDto);
+
         // Auto-assign rooms if needed
         $this->roomAssignmentService->assignRoomsIfNeeded($bookingCreateDto);
 

src/Service/RoomAssignmentService.php

@@ -110,4 +110,48 @@ class RoomAssignmentService
 
         return false;
     }
+
+    /**
+     * Validates and resets room assignments that reference rooms no longer selected.
+     *
+     * This method ensures room assignments remain valid after room selection changes in Step 1.
+     * When a user goes back to Step 1 and changes room selections, existing assignments may
+     * reference room IDs that are no longer in the selected rooms list. This method detects
+     * such invalid assignments and resets them to null.
+     *
+     * @param BookingDto $dto The booking DTO to validate
+     *
+     * @return bool True if any assignments were reset, false if all were valid
+     */
+    public function validateAndResetInvalidAssignments(BookingDto $dto): bool
+    {
+        $selectedRoomIds = $this->getSelectedRoomIds($dto);
+        $resetOccurred = false;
+
+        foreach ($dto->participants as $participant) {
+            if (null !== $participant->assignedRoomId && false === in_array($participant->assignedRoomId, $selectedRoomIds, true)) {
+                $participant->assignedRoomId = null;
+                $resetOccurred = true;
+            }
+        }
+
+        return $resetOccurred;
+    }
+
+    /**
+     * Gets the list of room IDs from currently selected rooms.
+     *
+     * @param BookingDto $dto The booking DTO containing room selections
+     *
+     * @return array<int> Array of selected room IDs
+     */
+    private function getSelectedRoomIds(BookingDto $dto): array
+    {
+        $ids = [];
+        foreach ($dto->getSelectedRooms() as $roomSelection) {
+            $ids[] = $roomSelection->id;
+        }
+
+        return $ids;
+    }
 }