SDK `permissions`: Workspace path is not detected correctly

Does this issue occur when all extensions are disabled?: Yes/No

ref https://github.com/microsoft/vscode/issues/329613

```
Version: 1.133.0-insider
Commit: 36cb0da730a61b80beb0e12f31c8f915ed0afebb
Date: 2026-08-07T10:58:22Z
Electron: 42.8.0
ElectronBuildId: 14845705
Chromium: 148.0.7778.280
Node.js: 24.18.0
V8: 14.8.178.38-electron.0
@github/copilot: 1.0.79-2
@github/copilot-sdk: 1.0.9-preview.3
OS: 36cb0da730a61b80beb0e12f31c8f915ed0afebb
```
Steps to Reproduce:

1. Add an `Edit()` or `Read()` selector into managed-settings.json with the workspace syntax (`/path/to/file` )
2. 🐛 Workspace from VS Code is not calculated correctly, causing incorrect allow/ask/deny behavior

Reproduce the issue using an Edit() or Read() selector in managed-settings.json with the workspace path syntax, then trace how the SDK calculates the VS Code workspace for permissions. Done means the workspace path is detected correctly and the selector produces the intended allow, ask, or deny behavior.

Written by the indexing model from the issue text.