Observer agents

A chat trigger normally behaves like a chatbot: someone writes a message, the agent replies to it, in the same place. Some jobs want a different shape. A review bot that watches a channel and only speaks up when something needs fixing. A moderation assistant that reports to a private channel the rest of the team can't see. A coach that gives one person feedback on their messages. In all of these the agent watches a conversation it isn't really part of, and that's what we call an observer.

The Discord, Slack and Telegram triggers all support this. Three optional keys together make the switch:

• from_users - handle only these authors. The filter runs before the model is called: everyone else's messages are dropped in the trigger and never reach the provider, so they cost no tokens.
• reply_channel (reply_chat on Telegram) - deliver replies to a dedicated channel instead of the source. Out-of-channel replies quote the triggering message and link back to it.
• allow_silence - let the agent say nothing. Instruct it in purpose to answer with exactly __NO_REPLY__ when it has no feedback; the trigger then posts nothing instead of a "looks fine" reply on every message. An empty reply also stays silent. On Discord, stray punctuation or whitespace around the sentinel is tolerated (cheap models like to add a trailing period); a sentinel buried in real content still posts.

You can use any of the three on their own. from_users alone gives you a bot that only listens to certain people; allow_silence alone gives you a chatbot that can decline to answer. An observer usually wants all three.

Example

A review bot that watches the pull-requests channel on Discord, reads Happy's messages, and posts feedback to a review channel when it has any:

handle: review-bot
description: Reviews Happy's PR summaries and flags anything risky.
model:
  provider: openai-compatible
  id: gpt-5.4-mini
purpose: |
  You watch PR summaries from Happy. If a summary mentions a risky change
  (migrations, auth, deletes), post a short note about what to double-check.
  If there is nothing to flag, reply with exactly __NO_REPLY__.
triggers:
  - type: discord
    channels: ["pull-requests"]
    from_users: ["happy"]
    reply_channel: "1522..."   # the review channel's id
    allow_silence: true

The same shape works on Slack (with Slack user ids in from_users) and on Telegram (with reply_chat instead of reply_channel).

Keep the typing indicator off

Discord's trigger can show a "typing…" indicator while a run is in flight (show_typing). Leave it off for an observer: an indicator that ends in no message reads as the bot changing its mind, and an observer stays silent most of the time.

Silent runs still leave a trace

Every run - replied or silent - lands in the agent's run history with its status, steps and tokens. When you're tuning the purpose to get the silence threshold right, the history is where you see what the agent decided on the messages it didn't answer.