### Describe the bug

In the agents tab, Playwright MCP browser_navigate never reaches a web server running on localhost. This might be a regression as I have seen this work.

Apologies if this is the wrong place to report this!

### Affected version

cloud

### Steps to reproduce the behavior

1. Create a new repo
2. Include test-ui.js
3. Start new agents tab. Ask co-pilot to start the app and take a screenshot

### Expected behavior

Co-pilot uses browser_navigate tool to access UI on localhost

### Additional context

test-ui.js:
```
#!/usr/bin/env node
/*
* test-ui.js — a minimal, zero-dependency, NO-AUTH frontend.
*
* Purpose: isolate whether the Copilot screenshot problem is Backstage-specific
* or lives in the MCP/screenshot pipeline. This serves a single static page with
* no sign-in, no catalog, no build step, no framework — just Node's built-in http.
*
* Run from the repo root: node test-ui.js
* Then open: http://127.0.0.1:8080 (also http://localhost:8080)
* Override the port with: PORT=1234 node test-ui.js
*/
const http = require('http');

const PORT = Number(process.env.PORT) || 8080;
// Loopback by default: a "normal" app that does NOT do the all-interfaces workaround.
// Flip to all-interfaces for comparison with: HOST=0.0.0.0 node test-ui.js
const HOST = process.env.HOST || '127.0.0.1';

const html = `

Test UI

TEST UI OK

No auth. Static page served by test-ui.js on port ${PORT}.

`;

const server = http.createServer((req, res) => {
res.writeHead(200, { 'Content-Type': 'text/html; charset=utf-8' });
res.end(html);
});

server.listen(PORT, HOST, () => {
console.log(`test-ui listening on http://${HOST}:${PORT}`);
console.log(`open http://127.0.0.1:${PORT} or http://localhost:${PORT}`);
});
```

browser_navigate エントリポイントから開始し、リポジトリのルートで node test-ui.js を実行します。localhost と 127.0.0.1 へのアクセスを比較し、その後、新しい agents タブで HOST=0.0.0.0 node test-ui.js を使って繰り返します。Playwright MCP がローカルページに到達し、Copilot がそのスクリーンショットを取得できれば完了です。

索引モデルが issue の本文から書いたものです。