Restore an archived person outside the school matched by the partner reference (externalReferenceId) written on the record. Same effects, errors and webhook as POST /externals/:id/restore.

The reference is not unique in legacy data, so the route restores only when it designates exactly one record to bring back: no record carries it → 404 EXTERNAL_NOT_FOUND; only active records carry it → 409 EXTERNAL_NOT_ARCHIVED; at least one active and at least one archived record carry it → 409 EXTERNAL_ALREADY_EXISTS with each active id under errors[].context.existingExternalId, nothing restored (restoring any of them would make the reference held twice); two or more archived records and no active one → 409 EXTERNAL_REFERENCE_NOT_UNIQUE with every archived id under errors[].context.externalId, most recently edited first, so the caller restores the right one by id; exactly one archived record → restored. As on the id route, an address held by another ACTIVE record answers 409 EXTERNAL_ALREADY_EXISTS with that record’s id under errors[0].context.existingExternalId.