Mark a message a channel shows once and keeps no copy of

go/asks/asks.go

@@ -318,6 +318,9 @@ type Message struct {
 	// To is the account linked as the operator on this kind, for a channel that verifies its sender: where
 	// the channel sends what is not a reply. The router's word, from its list; empty when none is linked.
 	To string `json:"to,omitempty"`
+	// Secret says the words carry something shown once (a link's code): the channel shows it and keeps no
+	// copy of it — no state, no history of its own.
+	Secret bool `json:"secret,omitempty"`
 }
 
 // Sender is who a channel's service says sent something: the account, the name it shows, and whether the