feat: indicate family insurance eligibility

src/Controller/Booking/Create/Step2ParticipantController.php

@@ -92,7 +92,9 @@ class Step2ParticipantController extends AbstractController
             return $this->redirectToRoute('app_booking_create_step_2');
         }
 
-        return $this->renderParticipantForm($form, $index, $bookingDto);
+        // Notifications were already cleared from the DTO above, so they have to be handed
+        // to the render path too - otherwise every invalid submission silently swallows them
+        return $this->renderParticipantForm($form, $index, $bookingDto, $notifications);
     }
 
     /**
@@ -124,17 +126,25 @@ class Step2ParticipantController extends AbstractController
         );
     }
 
-    /** @param FormInterface<mixed> $form */
+    /**
+     * @param FormInterface<mixed>                        $form
+     * @param array<array{type: string, message: string}> $notifications
+     */
     private function renderParticipantForm(
         FormInterface $form,
         int $index,
         BookingDto $bookingDto,
+        array $notifications = [],
     ): Response {
         $bookingCreateContext = $this->createContextFactory->create(
             $bookingDto,
             RoomPricingCalculator::PRICING_MODE_SELECTION
         );
 
+        // The rendered template includes _partials/_flashes.html.twig, so flashes added here
+        // are consumed by this very response instead of leaking into the next page
+        $this->addNotificationsAsFlashMessages($notifications);
+
         return $this->render('booking/create/step_2_participant.html.twig', [
             'form' => $form,
             'participantIndex' => $index,