Function refusal 

pub fn refusal(
    record: &Record<'_>,
    mutation: &DocumentMutation,
) -> Option<String>

Why a workspace refuses mutation, a change this process made to record of app_id, by what the app’s surface publishes, if it does: the check every receiver runs on its claims ([collab_types::check_claims_by_kind]), the grants aside, which the broker decides. None when this process holds no surface for the app: its receivers then hold the change until one arrives.