TypeError: n is not iterable

## Error

```
n is not iterable
```

## Stack trace

```
../app/javascript/components/profile/ContributionsSummary.tsx:46 in ContributionsSummary
Suspense
../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**: [TypeError: n is not iterable](https://thalamus-ai.sentry.io/issues/141693762/)
- **Culprit**: CANVAS_CUSTOM_POINTS.afterDraw(app/javascript/components/impact/chart-elements/plugins/canvas-custom-points)
- **First seen:** Aug 19, 2026

Start at app/javascript/components/profile/ContributionsSummary.tsx:46 and trace the data used by ContributionsSummary, then inspect app/javascript/components/impact/chart-elements/plugins/canvas-custom-points from the stack trace. Reproduce the error on the profile contributions view and confirm the fix prevents the TypeError without introducing a new failure.

Written by the indexing model from the issue text.