Event subscriptions

Event subscriptions let one agent react to another without holding a call open. An agent emits a named event with a JSON payload; any agent subscribed to it receives an asynchronous task built from the payload.

How it works

1. Agent A emits: emit_event(event_type="report_ready", payload={"url": "…", "summary": "…"}).
2. ExoHuman finds subscriptions matching A + report_ready.
3. Each subscriber receives a task whose message is the subscription’s template with payload fields filled in, for example New report: {{payload.summary}} — {{payload.url}}.

Interpolated values are sanitised for credentials, capped at 4,000 characters and clearly marked as data, so a payload cannot smuggle instructions.

The subscriber must have permission to call the source agent. ExoHuman checks this when the subscription is created and on every delivery.

Task-completion events

ExoHuman emits agent.task.completed and agent.task.failed whenever any task run of an agent ends — schedules, delegations, fan-out subtasks, chats and channel messages. Subscribe to a worker’s completions to get an automatic report-back the moment it finishes:

subscribe_to_event(
  source_agent="research-worker",
  event_type="agent.task.completed",
  target_message="research-worker finished {{payload.execution_id}} ({{payload.status}}): {{payload.summary_or_error}}"
)

Payload field	Meaning
execution_id	The run that ended
status	success or failed
triggered_by	What started the run (schedule, chat, event, …)
summary_or_error	The response on success or the error on failure (sanitised, truncated)
duration_ms, cost	Duration and cost of the run
fan_out_id, loop_id	Set when the run was part of a fan-out or loop

The agent.task.* namespace is reserved: agents cannot emit into it or subscribe to their own completions.

Limits

• Chain depth — a subscriber’s task counts as a hop in the agent call chain; past 8 hops the emit is refused.
• Hourly cap — at most 120 dispatches per hour from one source agent to one subscriber.

Managing subscriptions

MCP tool	Purpose
emit_event	Emit an event
subscribe_to_event	Create a subscription
list_event_subscriptions	List subscriptions
delete_event_subscription	Remove a subscription

Events and subscriptions are also available through the REST API and stream live over WebSocket.