TypeError: undefined is not an object (evaluating 'window.webkit.messageHandlers')

## Error

```
undefined is not an object (evaluating 'window.webkit.messageHandlers')
```

## Stack trace

```
https://exercism.org/:1 in sendDataToNative
https://exercism.org/:1
```

## Tracking Details
- **Project**: exercism-js
- **Sentry**: [TypeError: undefined is not an object (evaluating 'window.webkit.messageHandlers')](https://thalamus-ai.sentry.io/issues/144975089/)
- **Culprit**: sendDataToNative()
- **First seen:** Sep 4, 2026

Locate the sendDataToNative entry point in exercism-js and review how it accesses window.webkit.messageHandlers. Reproduce or trace the Sentry error in a browser context without that WebKit object, then verify the resulting behavior no longer raises this TypeError and that the native message path still works when available.

Written by the indexing model from the issue text.