React

# @json-render/react

React renderer that converts JSON specs into React component trees.

## Quick Start

```typescript
import { defineRegistry, Renderer } from "@json-render/react";
import { catalog } from "./catalog";

const { registry } = defineRegistry(catalog, {
  components: {
    Card: ({ props, children }) => <div>{props.title}{children}</div>,
  },
});

function App({ spec }) {
  return <Renderer spec={spec} registry={registry} />;
}
```

## Creating a Catalog

```typescript
import { defineCatalog } from "@json-render/core";
import { schema } from "@json-render/react/schema";
import { defineRegistry } from "@json-render/react";
import { z } from "zod";

// Create catalog with props schemas
export const catalog = defineCatalog(schema, {
  components: {
    Button: {
      props: z.object({
        label: z.string(),
        variant: z.enum(["primary", "secondary"]).nullable(),
      }),
      description: "Clickable button",
    },
    Card: {
      props: z.object({ title: z.string() }),
      description: "Card container with title",
    },
  },
});

// Define component implementations with type-safe props
const { registry } = defineRegistry(catalog, {
  components: {
    Button: ({ props }) => (
      <button className={props.variant}>{props.label}</button>
    ),
    Card: ({ props, children }) => (
      <div className="card">
        <h2>{props.title}</h2>
        {children}
      </div>
    ),
  },
});
```

## Spec Structure (Element Tree)

The React schema uses an element tree format:

```json
{
  "root": {
    "type": "Card",
    "props": { "title": "Hello" },
    "children": [
      { "type": "Button", "props": { "label": "Click me" } }
    ]
  }
}
```

## Visibility Conditions

Use `visible` on elements to show/hide based on state. New syntax: `{ "$state": "/path" }`, `{ "$state": "/path", "eq": value }`, `{ "$state": "/path", "not": true }`, `{ "$and": [cond1, cond2] }` for AND, `{ "$or": [cond1, cond2] }` for OR. Helpers: `visibility.when("/path")`, `visibility.unless("/path")`, `visibility.eq("/path", val)`, `visibility.and(cond1, cond2)`, `visibility.or(cond1, cond2)`.

## Providers

| Provider | Purpose |
|----------|---------|
| `StateProvider` | Share state across components (JSON Pointer paths). Accepts optional `store` prop for controlled mode. |
| `ActionProvider` | Handle actions dispatched via the event system |
| `VisibilityProvider` | Enable conditional rendering based on state |
| `ValidationProvider` | Form field validation |

### External Store (Controlled Mode)

Pass a `StateStore` to `StateProvider` (or `JSONUIProvider` / `createRenderer`) to use external state management (Redux, Zustand, XState, etc.):

```tsx
import { createStateStore, type StateStore } from "@json-render/react";

const store = createStateStore({ count: 0 });

<StateProvider store={store}>{children}</StateProvider>

// Mutate from anywhere — React re-renders automatically:
store.set("/count", 1);
```

When `store` is provided, `initialState` and `onStateChange` are ignored.

## Dynamic Prop Expressions

Any prop value can be a data-driven expression resolved by the renderer before components receive props:

- **`{ "$state": "/state/key" }`** - reads from state model (one-way read)
- **`{ "$bindState": "/path" }`** - two-way binding: reads from state and enables write-back. Use on the natural value prop (value, checked, pressed, etc.) of form components.
- **`{ "$bindItem": "field" }`** - two-way binding to a repeat item field. Use inside repeat scopes.
- **`{ "$cond": <condition>, "$then": <value>, "$else": <value> }`** - conditional value
- **`{ "$template": "Hello, ${/name}!" }`** - interpolates state values into strings
- **`{ "$computed": "fn", "args": { ... } }`** - calls reg