RangeError: Position 3086 is out of range for changeset of length 2713

## Error

```
Position 8 is out of range for changeset of length 6
```

## Stack trace

```
../app/javascript/components/misc/CodeMirror.tsx:29 in CodeMirror
Suspense
div
../app/javascript/components/common/Tab.tsx:55 in TabPanel
div
../app/javascript/components/editor/FileEditorCodeMirror.tsx:31 in FileEditorCodeMirror
div
div
../app/javascript/components/common/SplitPane.tsx:12 in SplitPane
div
```

## Tracking Details
- **Project**: exercism-js
- **Sentry**: [RangeError: Position 3086 is out of range for changeset of length 2713](https://thalamus-ai.sentry.io/issues/94587675/)
- **Culprit**: d(app/javascript/components/misc/CodeMirror)
- **First seen:** Feb 9, 2026