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

# System behavior

> How the system is designed to behave, so you can build on it.

export const productName = "Vainona";

This page describes how {productName} is designed to behave: what you can build around, and where the edges are. It is not a warranty or a service level agreement. The only commitments, remedies and limits of liability are those in your agreement with us. The [tradeoffs](/tradeoffs) page lists what the design gives up.

## Answers are judgments, not facts

An answer is an engine's judgment of your document, with a probability. It can be wrong, and the numbers on an engine's page, measured on our [conformance suite](/engines/index), may not match your data. Measure accuracy on your own documents with [outcomes](/guides/measure-improve-tune), and keep a person or a check in the loop wherever a wrong answer is costly.

## Your data

* **Writes.** A write is acknowledged only after it is committed to object storage.
* **Reads after a write.** After a write is acknowledged, a strong query sees the new revision and its attributes. Eventual queries can lag; see [tradeoffs](/tradeoffs).
* **Concurrent writes.** Writes to the same document are applied in the order they commit, and none is lost: two clients can `patch` or `append` to one document at once, and both changes stand. This holds when a server fails and another takes over its namespaces too. A write caught in that handover is refused with `rate_limited` and a `Retry-After` header, and retrying it is safe; the SDKs do so for you.
* **Training.** We do not fine-tune the engines we host on your data unless you opt in.

## Provenance

Every answer names its document revision, judgment version, engine version, and evaluation id. An answer reused because a change left its context the same keeps the id of the evaluation that computed it, which was for an earlier revision. An answer from a judgment that reads [related documents](/guides/related-documents) also names its watermark, except a `failed` one, which keeps its last good numbers without it, and its evaluation lists every related document it read, with its revision.

## Engines

* **Your judgment runs on the engine version you named** until you change it. Jev `current` cannot be pinned: it runs whatever Jev serves now. We detect changes in its behaviour and record them rather than hide them, and each answer's `engine_version` names the epoch of model behaviour that produced it. Other third-party engines are pinned as far as the vendor allows.
* **Versions do not change silently.** We intend to keep the engine versions we host available. If a version becomes unavailable, requests fail with a named error (`engine_version_unavailable`) rather than moving to another version.
* **Which subprocessor sees your data** depends on the engine you choose, and is written on that engine's page.

## When parts of the service are down

The data path is designed to keep working when sign-in, key management, billing or the dashboard is down: acknowledged writes stay durable, strong reads keep working, and existing judgments keep being evaluated. Creating or changing judgments may wait until those services recover.