Background agent worktrees do not work in Dev Containers

Does this issue occur when all extensions are disabled?: N/A

• VS Code Version: 1.109.0
• OS Version: Windows 11 (WSL2)

Attempting to use worktrees with Background agents doesn't work inside Dev Containers, due to permissions:

2026-02-05 14:56:41.915 [error] [ChatSessionWorktreeService][_createWorktree] Error creating worktree for isolation:: Failed to execute git {
  "exitCode": 128,
  "gitCommand": "worktree",
  "stdout": "",
  "stderr": "Preparing worktree (new branch 'copilot-worktree-2026-02-05T14-56-41')\nfatal: could not create leading directories of '/workspaces/my-repo.worktrees/copilot-worktree-2026-02-05T14-56-41/.git': Permission denied\n"
}

Steps to Reproduce:

1. Open a repository in a Dev Container
2. Attempt to use background agent from GitHub Copilot Chat

Interestingly, this error does not occur when using GitHub Codespaces, as the permissions in /workspaces are different.