One direct-message thread, rolled up. :participant is the other party as a map of name, handle, and avatar_url.
:participant
name
handle
avatar_url
@type t() :: %FoPost.InboxConversation{ account: term(), account_id: term(), conversation_id: term(), last_message_at: term(), last_message_outbound: term(), last_message_text: term(), message_count: term(), participant: term(), raw: term(), unread_count: term(), workspace_id: term() }