AI apps — assistant threads & streamed replies

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Slink covers Slack's AI-app surface end to end: the assistant events normalise like any other, and two helpers do the heavy lifting — a status line while you think, and a live streamed reply while you answer.

defmodule MyAssistant do
  use Slink
  alias Slink.Event

  @impl true
  def handle_event(%Event{type: :assistant_thread_started} = event, context) do
    Slink.API.set_suggested_prompts(
      context.bot_token,
      Event.channel(event),
      Event.thread_ts(event),
      [%{title: "Summarise this channel", message: "summarise the recent activity"}]
    )

    :ok
  end

  def handle_event(%Event{type: :message, subtype: nil} = event, context) do
    set_status(context, "is thinking…")
    stream_reply(context, MyLLM.stream(Event.text(event)))
  end

  def handle_event(_event, _context), do: :ok
end

What each piece does

  • :assistant_thread_started / :assistant_thread_context_changed — fired when a user opens the assistant pane. Event.channel/1, Event.user/1 and Event.thread_ts/1 resolve from the nested assistant_thread, so the accessors just work. The user's messages then arrive as ordinary :message events in that DM.
  • set_status/2 — the "is thinking…" line under the thread. Pass "" to clear; posting or streaming a reply clears it automatically.
  • stream_reply/3 — pass any enumerable of text chunks (an LLM token stream, a Stream, a list) and it renders as one live, progressively- updating message via chat.startStream / appendStream / stopStream. Chunks are batched (at most one append per :flush_ms, default 400ms) and sliced under Slack's 12k-per-append cap. Returns {:ok, ts}.
  • Thread titles — Slink.API.set_thread_title/4 names the conversation in the user's assistant history.

Graceful degradation

If the surface can't stream — the feature isn't enabled for the app, or the method errors — stream_reply/3 falls back to a single chat.postMessage with the full text. The reply always arrives; streaming is an enhancement.

Streaming into a channel (rather than the app's DM) additionally requires start: %{recipient_user_id: ..., recipient_team_id: ...}.

Requirements & verification

The assistant methods need the assistant:write scope and the Agents toggle in the app configuration; streaming runs under chat:write.

To check a real workspace, run the live smoke test — its AI step reports whether streaming is enabled without failing the run:

SLACK_BOT_TOKEN=xoxb-... mix slink.smoke C<your-test-channel>

For unit tests, Slink.Testing has assistant fixtures — event(:assistant_thread_started, ...) — and run/3 captures the startStream/appendStream/stopStream calls; see the Testing your bot guide.