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

# Execution and streaming

# Execution and streaming

***

## Core · Execution and streaming

> **Core principle** — Keep long work bounded while still delivering useful progress to the client.

Deadlines, cancellation, backpressure, SSE framing, and terminal states that behave under disconnects.

### Key concepts

<Columns cols={3}>
  <Card title="Backpressure" icon="sparkles">
    Bound buffers
  </Card>

  <Card title="Disconnect" icon="shield-check">
    Abort signal
  </Card>

  <Card title="Terminal" icon="gauge-high">
    Done or error event
  </Card>
</Columns>

### Boundary model

```mermaid placement="top-right" theme={null}
sequenceDiagram
    participant Client
    participant Handler
    participant Work
    Client->>Handler: Start stream
    Handler->>Work: Pass signal and deadline
    Work-->>Client: Progress event
    Client-->>Handler: Disconnect
    Handler->>Work: Abort and release
```

### Ownership matrix

| Concern      | Jeston/application boundary | Review signal                                      |
| ------------ | --------------------------- | -------------------------------------------------- |
| Backpressure | Bound buffers               | Never let a slow client grow memory without limit. |
| Disconnect   | Abort signal                | Stop model, database, and network work.            |
| Terminal     | Done or error event         | Let clients close cleanly.                         |

### Engineering considerations

Streaming increases responsiveness but also keeps resources open longer; its lifecycle must be more explicit than a normal response.

> **Design constraint**
>
> A stream is a resource lease, not an infinite response.

### Implementation notes

| Engineering move         | Guidance                                                             |
| ------------------------ | -------------------------------------------------------------------- |
| **Set a budget**         | Give the overall request and each dependency a deadline.             |
| **Define event shape**   | Choose event names, payloads, heartbeats, and terminal messages.     |
| **Propagate disconnect** | Abort work when the client leaves or the stream is no longer useful. |
| **Measure open work**    | Track active streams, duration, bytes, and cancellation reasons.     |

### Decision lens

| Mode      | Practical emphasis                                        |
| --------- | --------------------------------------------------------- |
| **SSE**   | Use explicit event framing and a terminal state.          |
| **Batch** | Prefer bounded chunks when clients do not need immediacy. |
| **Queue** | Move work beyond request lifetime into a durable job.     |

## Related topics

<Columns cols={3}>
  * [power-off · **Drain long work**](/jeston/jeston/operations/jobs-and-shutdown) — Read the focused guide for this boundary.
  * [brain · **Stream agent work**](/jeston/jeston/platform/ai-agents) — Read the focused guide for this boundary.
  * [chart-line · **Measure streams**](/jeston/jeston/platform/health-observability) — Read the focused guide for this boundary.
</Columns>

## References

[1]: https://github.com/jeffersoncampos12p-dev/jeston "Jeston source repository"

[2]: https://www.npmjs.com/package/@kvantjs/jeston "Jeston package on npm"

[3]: https://nodejs.org/api/http.html "Node.js HTTP API"

[4]: https://developer.mozilla.org/en-US/docs/Web/API/AbortSignal "AbortSignal Web API"

[5]: https://react.dev/reference/react-dom/server "React server rendering APIs"

[6]: https://www.typescriptlang.org/docs/handbook/intro.html "TypeScript handbook"