Function matches 

fn matches(
    subscription: &SlackSubscription,
    conversation: &SlackConversation,
    text: &str,
    ts: &str,
    user_id: &str,
    own_post: &dyn Fn(&str) -> bool,
) -> bool

Whether one subscription wants this message. forge posts as the user, so a message is refused by identity - its ts in the outbound ledger - and never by author: refusing every message the user wrote drops what Ved types himself, and a thread he is in then reads one-sided.