TypeError: Failed to execute 'createPolicy' on 'TrustedTypePolicyFactory': Policy with name "default" already exists.

## Error

```
Failed to execute 'createPolicy' on 'TrustedTypePolicyFactory': Policy with name "default" already exists.
```

## Stack trace

```
:4 in injectedFunction
:15
```

## Tracking Details
- **Project**: exercism-js
- **Sentry**: [TypeError: Failed to execute 'createPolicy' on 'TrustedTypePolicyFactory': Policy with name "default" already exists.](https://thalamus-ai.sentry.io/issues/144134777/)
- **Culprit**: injectedFunction()
- **First seen:** Sep 1, 2026

Start with the linked Sentry issue and its injectedFunction stack trace; the payload does not identify a source file or test. Trace the code that calls createPolicy and determine the intended behavior when the default policy already exists. Done means the reported error no longer occurs without breaking Trusted Types behavior, with a regression test if the relevant test location is found.

Written by the indexing model from the issue text.