<!-- source-hash: 6a8b6b64036a92c403c29835e73faf22 -->
React hook that resolves a branded OG placeholder image URL by reading runtime endpoints from `ChatRuntime` context and delegating to `buildOgPlaceholderUrl`.

## Key Components

### `UseOgPlaceholderUrlArgs`
Configuration interface for the hook:

| Property | Type | Default | Description |
|---|---|---|---|
| `title` | `string \| undefined \| null` | — | Text displayed on the placeholder image |
| `siteName` | `string` | `''` | Site name shown below the title |
| `aspect` | `'wide' \| 'square'` | `'wide'` | `'wide'` = 1200×630 social card; `'square'` = 1024×1024 for compact chat-inline slots |
| `enabled` | `boolean` | `true` | When `false`, returns `null` instead of a URL |

### `useOgPlaceholderUrl`
The single canonical hook for OG placeholder resolution. Reads `endpoints` from `ChatRuntime` context and passes them to `buildOgPlaceholderUrl`, which resolves the route base via:

1. Explicit `ogPlaceholderUrl` endpoint
2. Derived from `imageProxyUrlPrefix`
3. Same-origin fallback `/api/og-placeholder`

Returns a memoized `string | null`. Per-platform brand colors are resolved server-side by the route handler — nothing is baked into the URL.

## Usage Example

```typescript
import { useOgPlaceholderUrl } from './use-og-placeholder-url'

function LinkCard({ title, siteName }: { title: string; siteName: string }) {
  // Wide social-card placeholder (default)
  const placeholderUrl = useOgPlaceholderUrl({ title, siteName })

  // Square variant for compact chat-inline slots
  const squarePlaceholderUrl = useOgPlaceholderUrl({
    title,
    siteName,
    aspect: 'square',
  })

  // Conditionally disabled — returns null when no title is available
  const conditionalUrl = useOgPlaceholderUrl({
    title,
    enabled: Boolean(title),
  })

  return <img src={placeholderUrl ?? '/fallback.png'} alt={title} />
}
```

## Notes

- Replaces the older builder-injection pattern `useOgPlaceholder(buildUrl, …)` — callers no longer supply a URL builder.
- `useEntityCardPlaceholder` delegates here, ensuring all surfaces share one memo and one code path.
- Safe to call with a nullish `title`; returns `null` without throwing.

**Source:** [`use-og-placeholder-url.ts`](https://github.com/flamingo-stack/openframe-oss-lib/blob/main/use-og-placeholder-url.ts)