At-least-once delivery + idempotency

The Activity POSTs, then errors. Temporal retries. The receiver sees every POST. Without an idempotency key, every retry also lands.

Without Idempotency-Key

Attempt 1

→

Receiver

Attempt 2

→

Receiver

Attempt 3

→

Receiver

received

processed

deduped

With Idempotency-Key

Attempt 1

→

Receiver

Attempt 2

→

Receiver

Attempt 3

→

Receiver

received

processed

deduped

The fix: one line in activities.ts

Without (bug)

const headers: Record<string, string> = {
  'Content-Type': 'application/json',
  // no Idempotency-Key
};

With (fix)

const headers: Record<string, string> = {
  'Content-Type': 'application/json',
  'Idempotency-Key': `webhook:${req.eventId}`,
};