Every form and API route checks who you are before it does anything else.
Capability comes before nonce, everywhere — a valid nonce only proves a request was intentional, not that the requester is allowed to make it. Oiko Guard's own Settings_Page::save() shows the pattern exactly: `if ( ! current_user_can( 'manage_options' ) ) { wp_die(...); }` runs first, and only then does `check_admin_referer( 'oiko_guard_save_settings' )` fire. Every settings save, REST route and admin-post handler across every Oiko plugin follows this same order.