​
Reactions

React to a message by guid: 
await space.react(message.guid!, "like");
await space.react(message.guid!, "love", { remove: true });
Reactions also arrive on the signal feed: 
app.on("reaction", (signal, space) => {
  console.log(signal.reaction, signal.removed);
});

​
Replies

Thread a response under an existing message: 
await space.reply(message.guid!, "On it — give me a minute.");
Equivalent to space.send(text, { replyTo: message.guid }).

​
Platform support

ActioniMessageWhatsAppWhatsApp BusinessTerminal
react✓✓✓✓
reply✓✓✓✓
edit✓——✓
unsend✓——✓
Use platform narrowing when you need interface-specific behavior.