Partial update of an existing record by its ID. Only provided fields are modified.

• If a field is set to null → its value is reset.
• If a field is not provided → partial update, the field is ignored.

An unknown id, or one belonging to another school, answers 404 EXTERNAL_NOT_FOUND — never a silent success.

The email and the external reference are only checked for conflicts when they actually CHANGE: re-sending the record’s own values never fails, whatever duplicates the school already holds. A new address held by an ACTIVE record answers 409 EXTERNAL_ALREADY_EXISTS; one held only by an ARCHIVED record answers 409 EXTERNAL_ARCHIVED_EXISTS, both with the holder’s id under errors[0].context.existingExternalId.