Request body schema for updating an account (PUT /accounts/{account}).
Extends the shared Account schema. Updates are partial, so no field is required here, but email, address and city are re-declared as non-nullable: the model validates their presence on update (email unconditionally; address/city via require_address for accounts created on or after 2020-09-28), so sending them as null would be rejected. province is left nullable because its requirement is country-dependent. The response representation keeps Account (where these fields may be null).
parent_id is read-only here: an account's parent cannot be changed after creation.