> ## 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.

# Types reference

# Types reference

***

## Reference · Types

> **Reference purpose** — Use types to make lifecycle assumptions visible without pretending compile-time types validate network input.

A readable contract for contexts, handlers, responses, errors, and adapter capabilities.

### Key concepts

<Columns cols={3}>
  <Card title="Compile time" icon="sparkles">
    Developer feedback
  </Card>

  <Card title="Runtime" icon="shield-check">
    Boundary safety
  </Card>

  <Card title="Result" icon="gauge-high">
    Caller contract
  </Card>
</Columns>

### Reference model

```mermaid placement="top-right" theme={null}
flowchart LR
    wire[Network data] --> parse[Runtime validation]
    parse --> typed[Typed domain input]
    typed --> handler[Typed handler]
    handler --> result[Typed result]
```

### Contract summary

| Property     | Definition         | Review question                     |
| ------------ | ------------------ | ----------------------------------- |
| Compile time | Developer feedback | Catches shape mismatch.             |
| Runtime      | Boundary safety    | Catches hostile or malformed input. |
| Result       | Caller contract    | Makes success and failure explicit. |

### Interpretation

Types reduce accidental mismatch between layers, but boundary validation remains a runtime responsibility.

> **Reference note**
>
> A type is a promise made by code; validation is the evidence that the outside world kept it.

### Implementation notes

| Engineering move              | Guidance                                                            |
| ----------------------------- | ------------------------------------------------------------------- |
| **Type the context**          | Expose request ID, signal, deadline, params, and body deliberately. |
| **Separate input and output** | Do not reuse a domain type as an unvalidated network schema.        |
| **Model errors**              | Give callers stable categories and operators useful correlation.    |
| **Keep capabilities narrow**  | Adapters should implement only the operations they promise.         |

### Decision lens

| Mode               | Practical emphasis                                       |
| ------------------ | -------------------------------------------------------- |
| **Boundary types** | Pair static types with runtime parsing.                  |
| **Domain types**   | Represent invariants after validation.                   |
| **Adapter types**  | Describe capability and lifecycle, not vendor internals. |

## Related topics

<Columns cols={3}>
  * [globe · **Pair types with HTTP**](/jeston/jeston/reference/http-contracts) — Read the focused guide for this boundary.
  * [puzzle-piece · **Type capabilities**](/jeston/jeston/reference/adapters) — Read the focused guide for this boundary.
  * [brackets-curly · **Apply handlers**](/jeston/jeston/core/api-routes) — 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"