Function holochain_state::source_chain::current_countersigning_session

pub fn current_countersigning_session(
    txn: &Transaction<'_>, 
    author: Arc<AgentPubKey>
) -> SourceChainResult<Option<(EntryHash, CounterSigningSessionData)>>

Check if there is a current countersigning session and if so, return the session data and the entry hash.