VS Code Portable - GitHub Copilot SKILLS: SKILLS dialogue & user generated SKILLS ignores `COPILOT_HOME` (`.copilot/`) env variable

Does this issue occur when all extensions are disabled?: Yes

- VS Code Version:
Version: 1.133.0
Commit: a5b500951314efd502d07465bd138dfbd714a960
Date: 2026-08-11T22:14:08Z
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: 1.0.79-6
@github/copilot-sdk: 1.0.9
OS: a5b500951314efd502d07465bd138dfbd714a960

- OS Version: Windows 11 25H2

Recently https://github.com/microsoft/vscode/issues/314806 / https://github.com/microsoft/vscode/pull/314917 was implemented in VS Code, but it seems like the SKILLS feature of Copilot completely ignores that and is unable to find any skill files, steps to reproduce:

1. Create a portable VS Code installation (data folder inside VS Code root dir)
2. Add the ENV variable `COPILOT_HOME` and point it to the portable VS Code directory: `/.copilot`
3. Create the file `PortableVSCodeRootDir/.copilot/skills/test/SKILL.md`:
```md
---
name: test
description: Describe what this skill does and when to use it. Include keywords that help agents identify relevant tasks.
---

Define the functionality provided by this skill, including detailed instructions and examples
```
4. Check the VS Code Copilot customization tab "Skills" (it doesn't find the skill)