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Use a Fused-managed Slack connection to send allowlisted mentions into a Harnest agent. Fused owns provider credentials and verified event delivery. Harnest owns actor-scoped sessions, durable processing, and reply delivery intent.
Channel workers currently require the Harnest source checkout containing channel support. The runnable acceptance example is examples/channels/slack-agent, with its worker at examples/channels/slack_worker.py. It uses a deterministic Harnest Graph so you can verify transport without configuring a model or external tools. Replace it with your own served agent after the acceptance test passes.

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Prepare the Fused connection

Use an existing bucket your application is allowed to select. Bucket sharing does not grant secret administration or access to another installation’s events. For a Fused Managed App, select its exact managed auth reference; do not copy the broker’s client secret or signing secret into Harnest. Your immutable Python SDK version must select:
  • The reviewed Slack reply operation corresponding to chat.postMessage.
  • The explicit app_mention event and the applied webhook_attachment.
  • The intended bucket and managed OAuth reference, with app_mentions:read and chat:write consent for the approved bot installation.
Publish a new version if those selections change. Complete fresh consent if the existing grant lacks the reply permission. Install the generated Python package and use its documented module name and exact generated webhook enum value. Export that version’s Engine execution OpenAPI document and verify the reply operation accepts channel, text, thread_ts, reply_broadcast, unfurl_links, and unfurl_media in its physical input object. For managed events, the consumer’s webhook registration uses relay.source with the approved connection and operator-supplied broker registration. OAuth alone does not subscribe the application to events. See Fused webhook registration for ingress and attachment configuration.

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Configure one test conversation

Keep this JSON outside the agent source. Replace every placeholder with the reviewed application, generated SDK, and Slack identities. Use a dedicated, stable receiver name for this worker; another test subscriber should use its own name so it cannot consume this worker’s deliveries.
channel.json
Before the first run, set accept_after to the current Unix timestamp (for example, from date +%s). Keep that value across restarts. This excludes old retained mentions while allowing already-admitted work to recover. Load these values through your normal secret mechanism: Use TLS for remote Engine and agent connections. The loopback URLs above are local acceptance defaults. Neither runtime token belongs in channel.json.

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Start and test

From the Harnest source checkout, compile and serve the acceptance agent with CHANNEL_DATABASE_URL and CHANNEL_AGENT_TOKEN available:
In a second terminal with the installed generated SDK and the three runtime inputs above, start the worker:
Mention the bot in the allowlisted conversation. The agent replies in that message’s thread. A mention by another actor, in another conversation, or from another installation does not invoke the agent. Bot messages are ignored. The example agent authenticates the worker’s service credential before accepting its hashed actor header. For your own agent, provide equivalent authentication; request metadata does not establish user identity. Sessions include application, binding, installation, conversation, thread, and sender scope. Replies remain visible to participants in the Slack conversation.

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Delivery and recovery behavior

The generated SDK handler acknowledges Fused only after the task store commits input and processing intent together. A database failure produces a negative acknowledgement. Reply intent is persisted before calling Fused, and both Engine HTTP success and Slack’s ok result must pass before marking delivery complete. Use one worker per binding for the initial deployment. Claims are disjoint across replicas, but strict ordering of simultaneous messages is not guaranteed. This contract does not promise exactly-once external effects across process crashes. The worker reuses PostgresTaskStore, with channel.inbox and channel.outbox queues. Scoped get_task reads expose status and privacy-safe failure codes. Terminal task transitions remove private arguments; inspect the Harnest session and Fused execution receipt when reconciling an ambiguous outcome.