Full replacement: every active key omitted from the request is cleared. To set or clear
individual keys without disturbing the rest, use patch-customer-metadata instead. Null,
empty, and whitespace-only values clear one key. Unknown keys, archived keys, and
definitions not assigned to customers fail the entire request with a 400.
Metadata-only changes are recorded in the audit log but do not trigger customer.updated
webhooks or customer integration syncs.