Event bus (ADR-0005)

Every interesting thing — flow start, agent step, tool call, HITL gate, error — emits a typed event onto the bus.

Shape

Events follow CloudEvents 1.0. Required fields:

• id — ULID or UUIDv7
• source — package or component emitting
• type — reverse-DNS event name (io.agentskit.os.flow.step.completed)
• time — RFC3339 UTC timestamp
• data — typed payload (Zod-validated per type)

Why CloudEvents

• Bridges to message brokers (NATS, Kafka, Redis Streams) without re-encoding.
• Already understood by OTel, audit-log sinks, and most observability vendors.
• Forwards-compatible — extensions live in data without breaking parsers.

Bus bridges (M3+)

@agentskit/os-flow exports a bridge that forwards every flow event to the bus. Consumers include the audit emitter, OTel exporter, trace viewer, and cost-guard.

Source: ADR-0005.