plugin install fails with Access is denied (os error 5) on Windows for all sources

Bug Description

copilot plugin install fails 100% of the time on Windows 11 with:

Failed to install plugin: Error: Failed to install plugin: Access is denied. (os error 5)

It fails for a marketplace source (azure@azure-skills), a direct GitHub repo, and a local directory source — so it is not specific to one plugin or fetch method.

Version

• GitHub Copilot CLI: 1.0.71 (also seen on 1.0.70)
• OS: Windows 11 Enterprise 10.0.26200, x64
• git: 2.50.1.windows.1

Steps to reproduce

1. copilot plugin marketplace add microsoft/azure-skills
2. copilot plugin install azure@azure-skills
3. Fails with Access is denied. (os error 5)

Expected behavior

Plugin installs successfully.

Actual behavior

Install aborts. It creates an empty target folder under ~/.copilot/installed-plugins/ (e.g. azure-skills and _direct) then fails on its first file operation, before any file is written.

Investigation / ruled out

• Not permissions/sandbox: fails identically when run directly as the real user with Full Control over the entire ~/.copilot tree.
• Not Controlled Folder Access: Get-MpPreference shows EnableControlledFolderAccess = 0.
• Not git: git clone --depth 1 https://github.com/microsoft/azure-skills.git succeeds (1552 files).
• Not a lock: the leftover target folder can be freely renamed/deleted.
• Plain create/write/delete under installed-plugins and %TEMP% all succeed as the same user.
• Fails for both remote and local sources, immediately after the target dir is created.
• No detail is written to ~/.copilot/logs; the message is stderr-only and double-wrapped, hiding the offending path.

Suspected cause

A native filesystem op in the install/cache pipeline (likely remove_dir_all/rename/copy) returning Windows ERROR_ACCESS_DENIED — a common Rust-on-Windows failure against read-only files (e.g. git pack objects). Surfacing the actual path in the error would greatly help.

Workaround

copilot --plugin-dir <local-plugin-dir> loads the plugin fine, confirming only the install/copy path is broken.

Tái hiện lỗi bằng các lệnh cài đặt từ marketplace, repository trực tiếp và thư mục cục bộ, sau đó lần theo pipeline cài đặt/cache ngay sau khi thư mục đích được tạo. Xác định thao tác đầu tiên trên hệ thống tệp trả về ERROR_ACCESS_DENIED và đưa ra đường dẫn của nó; được coi là hoàn tất khi việc cài đặt plugin thành công trên Windows đối với từng nguồn và lỗi xác định đường dẫn gây ra vấn đề khi cài đặt thất bại.