SecurityError: Blocked a frame with origin "https://exercism.org" from accessing a cross-origin frame. Protocols, domains, and ports must match.

## Error

```
Blocked a frame with origin "https://exercism.org" from accessing a cross-origin frame. Protocols, domains, and ports must match.
```

## Stack trace

```
/users:333 in c
```

## Tracking Details
- **Project**: exercism-js
- **Sentry**: [SecurityError: Blocked a frame with origin "https://exercism.org" from accessing a cross-origin frame. Protocols, domains, and ports must match.](https://thalamus-ai.sentry.io/issues/139714969/)
- **Culprit**: c(users)
- **First seen:** Aug 9, 2026

Start with the /users:333 stack-trace location and review the linked Sentry report to identify the cross-origin frame access. Reproduce the SecurityError on the affected page, then verify that the error no longer occurs without breaking the page’s frame behavior.

Written by the indexing model from the issue text.