Collection new-session flow treats parent folder as a Git repository

[markweitzel]

Affected version

GitHub Copilot app 1.1.14 on macOS 26.6.2.

What happened?

A parent folder with no .git directory contains three direct child Git repositories, all on main. After adding the parent through Projects -> + -> Open folder, the app correctly registers it as a collection.

Opening New session for the collection shows generic single-repository controls (Project: collection name, Workspace: New worktree, Branch: main). The child repositories are not listed, so their branches and checkout modes cannot be selected.

Logs show the branch resolver targeting the non-Git parent:

Failed to get current branch path=~/gitrepos/spec-forge-all
error=git ["symbolic-ref", "HEAD"] failed:
fatal: not a git repository (or any of the parent directories): .git

The same failure occurs for git worktree list, for-each-ref, and git fetch against the parent.

Steps to reproduce

1. Create a parent folder containing multiple direct child Git repositories, with no .git at the parent.
2. Add the parent using Projects -> + -> Open folder.
3. Click New session for the collection.
4. Observe one branch selector for the parent and no child-repository list.

Expected behavior

Enumerate collection members and allow branch/checkout selection for each child. Run Git branch commands against each child, not the parent folder.

Additional context

Local repository is a partial workaround but does not restore isolated multi-repository worktrees or per-repository branch selection. Related but narrower: #786 covers per-repository default branches.