Using a notification ledger as an RPC channel has side effects

When you tunnel a host-to-client request (e.g. 'open this file') through an existing notification system because no other channel exists, check what the daemon does on create: it may set an unread/attention marker per terminal that ack never clears, overwrite a real pending marker (like an agent waiting for input), and consume slots in a fixed-capacity ledger. Also make the ack carry the outcome: if the receiver acks refused requests the same way as accepted ones, the sender reports success for nothing. And measure staleness by receiver arrival time, not sender timestamps, or clock skew makes every request stale.