204 No Content. The signal is ephemeral: it is pushed to active devices and never enters the durable event log. The agent must be a participant in the conversation.
Add a short status line with label:
Conversations
Typing indicators
Show live typing state while your backend prepares a reply.
Show a typing indicator while your backend is working:
Relay returns
Labels can contain up to 80 characters.
Sending a message clears the visible indicator. When a reply may stop before sending, put the stop request in cleanup logic so the conversation returns to its resting state.
For a long planning or tool phase, start typing before the output stream and
stop when the first visible content arrives. See Streaming replies.