Events & streaming

Everything an agent does is recorded as an ordered stream of events. Each event has a monotonically increasing seq within its session, so the stream is fully resumable: reconnect from the last seq you saw and never miss or duplicate an event. Because every event is sequence-keyed, a dropped connection is not a lost event — you reconnect with the last seq you handled and the stream picks up exactly where you left off:

   session events, ordered by seq
   ──▶ 125 ─ 126 ─ 127 ─ 128 ─ 129 ─▶ (live tail)
                             ▲
        reconnect with from_seq = last seq you handled
        replay from 0 for a fresh consumer · no gaps, no duplicates

Event shape

Events follow a {domain}.{action} naming scheme.

{
  "seq": 128,
  "session_id": "ses_01H...",
  "type": "tool.completed",
  "created_at": "2026-08-20T23:14:02.140Z",
  "data": { "name": "bash", "exit_code": 0, "duration_ms": 812 }
}

Streaming

Streams are delivered as Server-Sent Events. Pass a from_seq to replay from a point in history — new consumers pass 0 to get the whole session.

# Stream live; append new events as they arrive
vetta session stream --session $SID --from-seq 0

for await (const e of session.stream({ fromSeq: lastSeq })) {
  lastSeq = e.seq;
  handle(e);
}

curl -N "https://api.vetta.sh/v1/sessions/$SID/events?from_seq=0" \
  -H "authorization: Bearer $VETTA_API_KEY" \
  -H "accept: text/event-stream"

Reading history

Events are also available as a paginated list for auditing or replay without a live connection.

CLI

vetta session events --session $SID --limit 100

Sending events in

You drive a session by sending events too — a user message, a tool confirmation, or an interrupt.

TypeScript

await session.send("Refund order #4821");          // user.message
await session.confirm(toolCallId);                  // tool.confirm  (ask-policy confirmation)
await vetta.sessions.interrupt(session.id);         // session.interrupt

Common event types

Type	Meaning
`session.running`	The agent started a turn.
`session.idle`	The turn yielded control and the session is waiting. Carries a `stop_reason`.
`session.completed`	The agent declared the task done.
`session.usage`	A cumulative cost/usage snapshot (`token_usage`, `consumed_micro_usd`, `active_seconds`, `tool_calls`), emitted before every idle or terminal transition. See Observability.
`message.delta`	A chunk of assistant text.
`message.completed`	An assistant message finished.
`tool.started`	A tool call began.
`tool.confirm`	A tool gated by an `ask` policy is waiting on your allow/deny.
`tool.completed`	A tool call finished (success or error).
`budget.exceeded`	A call was refused because it would breach the cap.
`budget.paused`	The session paused at its budget cap.

See the full list in the Event reference.

Next: completion window

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Agent

Running an agent

Agent capabilities

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Identity

Team

Events & streaming

Event shape

Streaming

Reading history

Sending events in

Common event types

Next: completion window

​Event shape

​Streaming

​Reading history

​Sending events in

​Common event types

Next: completion window

Event shape

Streaming

Reading history

Sending events in

Common event types