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

# Extension points

> Concrete adapters and abstract interfaces at the pinned implementation commit.

LangState separates reusable state primitives from application-specific behavior. The table below distinguishes contracts from implementations.

| Area                 | Contract                      | Included implementation                               | Application work                                          |
| -------------------- | ----------------------------- | ----------------------------------------------------- | --------------------------------------------------------- |
| Schema extraction    | `BaseSpecExtractor`           | `OpenAPIReader`                                       | Choose the root entity and supply a local spec            |
| Mutation             | `BaseMutator[TContext]`       | `LLMMutator`                                          | Supply `BaseLLMClient` or write another mutator           |
| Canonical projection | `BaseProjectorCanonicalState` | None                                                  | Resolve candidates, validate, and decide action readiness |
| UI projection        | `BaseProjectorUI`             | None                                                  | Generate prompts/components for the chosen UI             |
| Action               | `BaseAction`                  | None                                                  | Execute domain behavior and return `ActionResult`         |
| Evaluation           | `BaseEvaluator`               | `Evaluator` comparison base and `LLMEvaluator` runner | Provide mutator and expected states                       |
| Repository           | `BaseStateRepository[TState]` | `InMemoryStateRepository`                             | Implement durable storage when needed                     |
| Snapshot store       | `BaseSnapshotStore[TState]`   | `InMemorySnapshotStore`                               | Implement durable history and retention when needed       |
| Orchestrator         | `LangState[TContext]`         | None                                                  | Implement lifecycle and component coordination            |

## Mutator contract

`BaseMutator.mutate(context)` is asynchronous and returns `MutationResult`. The included `LLMMutator`:

1. copies the input `InterpretiveState`;
2. asks the supplied `BaseLLMClient` for a JSON array of extractions;
3. validates each extraction;
4. appends a `ValueConfidence` candidate; and
5. replaces the field's latest `Inference`.

Provider authentication, retries, structured-output enforcement, rate limiting, and telemetry belong to the client implementation or application layer.

## Projector contracts

`BaseProjectorCanonicalState` requires `project()` and `can_trigger_action()`. Its schema supports resolution strategy, confidence threshold, validation errors, fields requiring confirmation, and triggered-action identifiers.

`BaseProjectorUI` requires `project()`, `generate_prompt()`, and `map_field_to_component()`. UI model types are data contracts; no renderer is bundled.

## Keep orchestration ownership explicit

When composing extensions, decide which layer owns the loop, current state, authentication, billing, persistence, and retries. The base `LangState` class stores references but does not silently take ownership of those concerns.