TypeError: Cannot read properties of undefined (reading 'length')

## Error

```
Cannot read properties of undefined (reading 'length')
```

## Stack trace

```
../node_modules/@codemirror/view/dist/index.js:627 in ChildCursor.findPos
../node_modules/@codemirror/view/dist/index.js:3087 in DocView.domAtPos
../node_modules/@codemirror/view/dist/index.js:2942 in DocView.updateSelection
../node_modules/@codemirror/view/dist/index.js:7571 in EditorView.update
../node_modules/@codemirror/view/dist/index.js:7465 in this.dispatchTransactions
../node_modules/@codemirror/view/dist/index.js:7489 in EditorView.dispatch
../node_modules/@codemirror/autocomplete/dist/index.js:1230 in completionPlugin.accept
../node_modules/@codemirror/autocomplete/dist/index.js:1181 in completionPlugin.scheduleAccept
../node_modules/@codemirror/autocomplete/dist/index.js:1172 in
```

## Tracking Details
- **Project**: exercism-js
- **Sentry**: [TypeError: Cannot read properties of undefined (reading 'length')](https://thalamus-ai.sentry.io/issues/101663055/)
- **Culprit**: ChildCursor.findPos(@codemirror/view/dist/index)
- **First seen:** Mar 8, 2026