Your AI agent re-sends the email on retry: an outbox for side effects

Description and use

The outbox pattern records intent as state and performs I/O after commit, eliminating duplicate emails on retries and replays.

Problem

Agent frameworks that perform I/O inside a step cause duplicate side effects when the run is retried, resumed, or replayed.

Outcome

Using an outbox pattern with reactifact prevents duplicate emails on retries, resumes, and replays, while preserving idempotency and enabling accurate replay without side effects.

Workflow

• 1. Define a produce that records a PendingAction intent using effects.act() instead of performing I/O.
• 2. Commit the produce’s effects atomically with other state changes.
• 3. After commit, the runtime dispatcher processes each pending intent once per stable id.
• 4. The dispatcher performs the actual I/O (e.g., send email) and records the outcome as state.

Evidence

Most agent frameworks model a step as "do some work, then call the tools."

Source

The outbox inverts the order: 1. The produce records an intent — an artifact called PendingAction — and does no I/O.

Source

Replay reconstructs the answer without re‑sending anything.

Source

The runtime drains the outbox after each generation's commit, marking each action dispatched or failed.

Source