WSL remote sessions can time out or show stale Files and Changes state for large repositories

Description

When a Copilot remote session uses an existing large Git repository inside WSL, repository initialization and UI state can fail or become stale.

Steps to reproduce

1. Open a large existing Git repository inside WSL.
2. Start a Copilot remote session using that checkout.
3. Open the Files or Changes panel.
4. Create or modify a file.

Actual behavior

• Session startup may time out during recursive filesystem watching.
• The Files panel may fail to populate.
• Branch information or uncommitted changes may be missing.
• The Changes panel can remain empty after its initial repository scan times out.
• Later filesystem changes may not refresh the displayed state.

Expected behavior

• Remote sessions should work directly with existing WSL checkouts.
• Startup should not require enumerating the entire repository when only configuration files need monitoring.
• Files, branch information, and Git changes should load asynchronously and refresh reliably.
• Slow initial Git operations should not cause an empty state to be cached permanently.
• Users should not need a separate clone or worktree as a workaround.

Suggested improvements

• Limit configuration-file watchers to the relevant directories.
• Avoid synchronous recursive traversal during session startup.
• Make changeset calculation asynchronous and tolerant of slow Git operations.
• Retry or refresh after an initial timeout.
• Surface diagnostics when filesystem watching or Git status exceeds a timeout.

No source files or tests are named in the issue. Start by reproducing the timeout with a large Git repository in WSL, then trace remote-session startup, filesystem watching, and Changes initialization; done means Files, branch data, and Git changes load and refresh reliably without requiring a separate clone or worktree.