Parent folder is forced into a collection and creates worktrees for every nested repository

### Short summary

_No response_

### Affected version or release

1.0.71-0

### Installation context

_No response_

### What happened?

Parent folder is forced into a collection and creates worktrees for every nested repository

Product: GitHub Copilot app
Version: 1.0.71-0
Operating system: Windows
Severity: High — excessive startup time and disk consumption

Description

Adding C:\DEV\workspace as a project now causes the Copilot app to discover approximately 500 independent Git repositories beneath that folder and automatically classify the project as a collection. Starting a session then attempts to create a new Git worktree for every discovered repository.

This makes the project take a very long time to start and consumes a large amount of disk space. The same parent-folder workflow worked previously without creating worktrees for every nested repository, so this appears to be a regression.

Steps to reproduce

Create a directory containing many independent Git repositories in nested folders.
In the Copilot app, add the parent directory as a local project; for example, C:\DEV\workspace.
Observe that the app automatically classifies it as a collection.
Start a new session for that project.
Observe that the app attempts to create a worktree for every nested repository.

Expected behavior

The app should allow the selected parent directory to be used as one in-place local workspace without creating worktrees for nested repositories. Collection behavior and bulk worktree creation should require explicit opt-in. At minimum, the app should offer a persistent Local repository / no worktrees option for the entire folder before performing any disk-intensive operation.

Actual behavior

The folder is automatically converted into a collection, and starting a session initiates worktree creation across approximately 500 repositories. There is no visible project-level option to disable collection detection or force all sessions to run in place.

Impact

The workspace project is effectively unusable. Session startup takes a long time, and bulk worktree creation consumes substantial disk space. The only current workaround is to remove the parent project and configure repositories individually, which loses the previous whole-workspace workflow.

### Steps to reproduce

_No response_

### Expected behavior

_No response_

### Additional context

_No response_

No source files, tests, or entry points are identified. Reproduce the issue on Windows with a parent folder containing nested Git repositories, then trace collection detection and session startup; done means the parent folder can remain an in-place workspace without creating nested worktrees unless explicitly enabled.

Written by the indexing model from the issue text.