fix: correctly handle email uniqueness by excluding the applicant from validation

src/Form/Model/ParticipantEditDto.php

@@ -121,15 +121,22 @@ class ParticipantEditDto
     }
 
     /**
-     * Validates that adult participants have unique email addresses.
+     * Validates that non-applicant adult participants have unique email addresses.
      *
-     * Children (under 16) are exempt from this validation and can share
+     * Exempt from validation:
-     * email addresses with adults. Email comparison is case-insensitive
+     * - Applicant (index 0): Can share email with dependents they're booking for
-     * and whitespace is normalized.
+     * - Children (under 16): Can share email addresses with adults
+     *
+     * Email comparison is case-insensitive and whitespace is normalized.
      */
     #[Assert\Callback(groups: ['booking_create', 'booking_edit'])]
     public function validateEmailUniqueness(ExecutionContextInterface $context): void
     {
+        // Skip validation for applicant (index 0) - applicant's email can be shared with dependents
+        if (true === $this->participant->isApplicant()) {
+            return;
+        }
+
         // Skip validation for children (under 16)
         if (true === $this->participant->isChild()) {
             return;