NotFoundError: The object can not be found here.

## Error

```
The object can not be found here.
```

## Stack trace

```
../app/javascript/components/editor/AssistantChat/AssistantChatStartState.tsx:51 in AssistantChatStartState
../app/javascript/components/editor/AssistantChat/AssistantChatPanel.tsx:42 in AssistantChatContent
../app/javascript/components/common/Tab.tsx:58 in TabPanel
../app/javascript/components/common/SplitPane.tsx:16 in SplitPane
../app/javascript/components/Editor.tsx:92 in Editor_default
../node_modules/@sentry/react/src/errorboundary.tsx:101 in new ErrorBoundary
../node_modules/@tanstack/react-query/src/QueryClientProvider.tsx:30 in QueryClientProvider
```

## Tracking Details
- **Project**: exercism-js
- **Sentry**: [NotFoundError: The object can not be found here.](https://thalamus-ai.sentry.io/issues/145152165/)
- **Culprit**: removeChild([native code])
- **First seen:** Sep 5, 2026

Start at app/javascript/components/editor/AssistantChat/AssistantChatStartState.tsx:51, then trace the surrounding AssistantChatPanel.tsx and Editor.tsx entries shown in the stack trace. Reproduce the AssistantChat error and inspect the removeChild failure reported by Sentry. Done means opening the affected editor state no longer produces “The object can not be found here.”

Written by the indexing model from the issue text.