AdGuard Assistant breaks ChatGPT embedded app widgets with duplicate `SafariAppExtensionPage` declaration

### Please answer the following questions for yourself before submitting an issue

- [x] Filters were updated before reproducing an issue
- [x] I checked the [knowledge base](https://adguard.com/kb/) and found no answer
- [x] I checked to make sure that this issue has not already been filed

### AdGuard version

2.19.0.2258 release

### Browser version

Safari 26.5.2 (21624.2.5.11.8)

### OS version

macOS 26.5.2 (25F84)

### Ad Blocking

_No response_

### Privacy

_No response_

### Social

_No response_

### Annoyances

_No response_

### Security

_No response_

### Other

_No response_

### Language-specific

_No response_

### Which DNS server do you use?

AdGuard DNS

### DNS protocol

None

### Custom DNS

_No response_

### What Stealth Mode options do you have enabled?

_No response_

### Support ticket ID

_No response_

### Issue Details

Steps to reproduce:
1. Enable AdGuard protection and the bundled AdGuard Assistant in Safari Settings → Extensions.
2. Open https://chatgpt.com in Safari.
3. Open a chat with access to an embedded app such as Spotify.
4. Submit a new request that generates a Spotify app card.
5. Observe that the card frame appears, but its embedded content does not render.
6. Open Safari Web Inspector and inspect the console.
7. Observe: `SyntaxError: Can't create duplicate variable: 'SafariAppExtensionPage'`
8. Disable only AdGuard Assistant in Safari Settings → Extensions, while leaving AdGuard filtering and its content blockers enabled.
9. Reload ChatGPT and generate another new Spotify card.
10. Observe that the newly generated card renders successfully.

Reproduction frequency: consistent during controlled testing when AdGuard Assistant was enabled. After disabling Assistant, newly generated cards rendered successfully in repeated tests.

### Expected Behavior

AdGuard Assistant should initialize safely in the page and its embedded frames. If its initialization code is invoked more than once, repeated initialization should be idempotent and should not terminate other JavaScript running in the frame.

### Actual Behavior

Safari throws the duplicate-variable SyntaxError and the card stays blank. Disabling only Assistant restores new-card rendering.

### Screenshots

_No response_

### Additional Information

Affected extension:
- Bundle ID: `com.adguard.mac.adguard.safari-assistant`
- Version: `2.19.0.2258`
- Bundle version: `2258`

Network observations:
- The `web-sandbox.oaiusercontent.com` frame document loaded.
- Assets served by `web-sandbox.oaiusercontent.com` loaded.
- Spotify `styles.css` and `script.js` were requested from `duet-mcp-cdn.spotifycdn.com`.

This therefore does not appear to be solely a blocked-request failure.

Current workaround:
- Disable only AdGuard Assistant in Safari.
- Keep AdGuard filtering and content blockers enabled.
- Use these user rules:

```adblock
@@||chatgpt.com^$important,document
@@||web-sandbox.oaiusercontent.com^$content
```

These rules alone did not address the extension JavaScript error while Assistant was enabled. Disabling Assistant was the change that resolved live rendering.

This report concerns newly generated cards failing while AdGuard Assistant is enabled. A separate ChatGPT issue can cause older app cards to be blank after reopening a browser; that behavior occurs in other browsers and is excluded from this report.

Possibly related discussion:
https://community.openai.com/t/widget-not-loading-since-yesterday-march-4/1375747