Signals

A signal is an unassigned external event. The workflow waits; a product API delivers the payload with a deduplication key.

final receipt = await flow.waitForSignal(
  paymentReceived,
  id: 'payment',
);

Signals delivered before waitForSignal are buffered. Duplicate deliveries with the same idempotency key do not append a second history event.

JSON documents use a signal step and an inputBinding for the expected payload shape.

When to Use a Signal vs a User Task

Use	Why
User task	Work is assigned and must appear in an inbox
Signal	An external system or webhook reports a fact

Do not hide automated work inside a user-task completion handler. Start the external job in a service task, then wait for a signal.

See Also

• Signals execution
• Service API