TypeError: t.entries.at is not a function

## Error

```
t.entries.at is not a function
```

## Stack trace

```
/beacon.min.js:1
/beacon.min.js:1
/beacon.min.js:1
/beacon.min.js:1
/beacon.min.js:1
/beacon.min.js:1 in B
/beacon.min.js:1 in o
../node_modules/@sentry/browser/src/helpers.ts:117 in sentryWrapped
```

## Tracking Details
- **Project**: exercism-js
- **Sentry**: [TypeError: t.entries.at is not a function](https://thalamus-ai.sentry.io/issues/129068642/)
- **Culprit**: ?(beacon)
- **First seen:** Jun 19, 2026

Start with the Sentry report and the stack trace pointing to beacon.min.js and @sentry/browser/src/helpers.ts:117. Identify which browser or runtime produces the TypeError and trace the related exercism-js frontend entry point; done means the cause is confirmed and the error no longer occurs in the affected environment.

Written by the indexing model from the issue text.