bug: browser_snapshot fails on CSP-sandboxed text documents

What's broken

On Paseo Desktop, browser_snapshot fails on a plain-text document served with a CSP sandbox directive. browser_evaluate fails on the same tab with the same generic script-execution error.

A control tab opened on https://example.com immediately afterward succeeds with both tools on the same machine and display state, so this is URL/document-specific rather than the separate Windows painted-frame screenshot issue reported in #3824.

Expected: browser_snapshot returns an accessibility snapshot or plain-text representation, or returns a specific structured unsupported error.

Actual:

Error invoking remote method 'paseo:browser:execute-automation-command': Error: Script failed to execute, this normally means an error was thrown. Check the renderer console for the error.

Steps to reproduce

1. Start Paseo Desktop v0.5.2 on Windows.
2. Open this URL with browser_new_tab: https://raw.githubusercontent.com/stayhydated/skills/master/skills/manage-workspace-agents-md/SKILL.md
3. Wait for the URL to load.
4. Call browser_snapshot.
5. Observe the generic script-execution error above.
6. Call browser_evaluate to read document.body.innerText.
7. Observe:
   复制

   Script failed to execute, this normally means an error was thrown. Check the renderer console for the error.

8. Open https://example.com as a control and repeat both calls.
9. Observe that browser_snapshot succeeds (9 nodes / 1 ref) and browser_evaluate returns:
   json复制

   {"readyState":"complete","hidden":false,"visibilityState":"visible","text":"Example Domain\n\nThis domain is for use in documentation examples without needing permission. Avoid use in operations.\n\nLearn more"}

The failing URL responds with:

StatusCode: 200
Content-Type: text/plain; charset=utf-8
Content-Disposition:
X-Content-Type-Options: nosniff
Content-Security-Policy: default-src 'none'; style-src 'unsafe-inline'; sandbox

Where did this happen

Paseo Desktop (Electron), using Paseo's native browser tools.

Paseo version

0.5.2

OS version

Windows 11 Pro x64, build 26200

Agent provider

Codex

Provider configuration

No special browser configuration. The calls were made through Paseo's local native browser MCP tools.

Logs

The webview registered successfully, followed by Chromium rejecting script execution because the document frame is sandboxed without allow-scripts:

[2026-08-25 12:20:44.997] [info]  [browser-webview] registered {
  browserId: '233bce43-ccbf-4ecc-afdc-cc9d8c86fbe1',
  webContentsId: 20,
  registeredBrowserIds: [ '233bce43-ccbf-4ecc-afdc-cc9d8c86fbe1' ]
}
[2026-08-25 12:20:47.808] [error] Blocked script execution in 'https://raw.githubusercontent.com/stayhydated/skills/master/skills/manage-workspace-agents-md/SKILL.md' because the document's frame is sandboxed and the 'allow-scripts' permission is not set.
[2026-08-25 12:20:55.925] [error] Blocked script execution in 'https://raw.githubusercontent.com/stayhydated/skills/master/skills/manage-workspace-agents-md/SKILL.md' because the document's frame is sandboxed and the 'allow-scripts' permission is not set.
[2026-08-25 12:33:48.325] [error] Blocked script execution in 'https://raw.githubusercontent.com/stayhydated/skills/master/skills/manage-workspace-agents-md/SKILL.md' because the document's frame is sandboxed and the 'allow-scripts' permission is not set.
[2026-08-25 12:33:52.748] [error] Blocked script execution in 'https://raw.githubusercontent.com/stayhydated/skills/master/skills/manage-workspace-agents-md/SKILL.md' because the document's frame is sandboxed and the 'allow-scripts' permission is not set.

Screenshots or video

None. This is a tool-response failure with no visual UI defect; the raw tool outputs and renderer logs are included above.