> ## Documentation Index
> Fetch the complete documentation index at: https://docs.agenticenv.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Durable Engine

> Build a caller-owned durable-go engine for payload encryption, journal MAC, and stable step-token keys

Uses `local.WithLocalConfig(&local.LocalConfig{Engine: engine})` instead of the SDK-built default engine. You create and own the [durable-go](https://github.com/agenticenv/durable-go) engine — required for AES-GCM payload encryption, journal MAC, and a step-token key that survives a process restart. Same split as [`temporal.WithTemporalClient`](/examples/temporal-client).

Source: [`examples/agent_with_durable_engine/`](https://github.com/agenticenv/agent-sdk-go/tree/main/examples/agent_with_durable_engine)

## What it demonstrates

* `durable.NewEngine` with `WithPayloadCodec`, `WithJournalMACKey`, `WithStepTokenKey`
* `local.WithLocalConfig(&local.LocalConfig{Engine: engine})` on `NewAgent`
* Caller-owned engine lifecycle (`defer engine.Close()` — `a.Close()` does not close it)

## Run

From `examples/` (local runtime only — no Temporal or Restate):

```bash theme={null}
go run ./agent_with_durable_engine "Hello, what can you do?"
```

Optional env (hex). If unset, the example generates random keys and a temp `dataDir`:

| Variable | Purpose |
| - | - |
| `DURABLE_PAYLOAD_KEY` | AES-GCM key (16/24/32 bytes hex) |
| `DURABLE_JOURNAL_MAC_KEY` | Journal HMAC key |
| `DURABLE_STEP_TOKEN_KEY` | Approval token key (survives restart) |
| `DURABLE_DATA_DIR` | Journal directory (default: temp dir, deleted on exit) |

## Key code

```go theme={null}
engine, err := durable.NewEngine(ctx, dataDir,
    durable.WithPayloadCodec(codec),
    durable.WithJournalMACKey(macKey),
    durable.WithStepTokenKey(tokenKey),
)
defer engine.Close()

a, err := agent.NewAgent(
    local.WithLocalConfig(&local.LocalConfig{Engine: engine}),
    agent.WithLLMClient(llmClient),
)
```

For simple local dev without encryption or a stable token key, omit `Engine` — see [In-Process runtime](/runtimes/in-process).

## Expected output

```
I'm a helpful assistant powered by an LLM. I can answer questions, help with tasks,
and have multi-turn conversations. What would you like to explore?
```

The response is identical to the simple-agent — the difference is the journal (encrypted + MAC-signed) and caller-owned engine lifecycle.

## Learn more

<CardGroup cols={2}>
  <Card title="In-Process Runtime" icon="laptop" href="/runtimes/in-process" horizontal>
    SDK-built knobs vs caller-owned Engine
  </Card>

  <Card title="Temporal Client" icon="server" href="/examples/temporal-client" horizontal>
    Same ownership pattern for Temporal
  </Card>
</CardGroup>