fix: stop counting held seats in edit usage

src/Service/ServiceAvailabilityCalculator.php

@@ -219,6 +219,10 @@ class ServiceAvailabilityCalculator
     /**
      * Calculate how many times each service has been selected by other participants.
      *
+     * Only new selections count. In edit mode the form is prefilled with the live booking, whose
+     * seats BusPro has already deducted from frei; counting them again would report a contingent
+     * as exhausted while seats are still free.
+     *
      * @param BookingDto $bookingDto              The booking data with participant selections
      * @param int        $currentParticipantIndex The index of the participant currently filling the form
      *
@@ -238,6 +242,10 @@ class ServiceAvailabilityCalculator
             $participantUsage = $this->countParticipantServiceUsage($participant);
 
             foreach ($participantUsage as $serviceId => $count) {
+                if (null !== $bookingDto->booking && $bookingDto->booking->hasServiceForParticipant($index, $serviceId)) {
+                    --$count;
+                }
+
                 $serviceUsage[$serviceId] = ($serviceUsage[$serviceId] ?? 0) + $count;
             }
         }