WSL session creation fails during host authentication: could not verify GitHub identity

### Short summary

WSL session creation fails during host authentication with `rpc error -32603: internal error: could not verify GitHub identity`.

### Affected version or release

GitHub Copilot app v1.1.14 (commit `0d498e8`)

### Installation context

- GitHub Copilot app installed locally on Windows 11 Enterprise, x86_64
- WSL hosts (Preview) enabled
- WSL 2.7.12.0
- Ubuntu 24.04.4 LTS on WSL2
- `copilotd` 0.7.3 (the version pinned by the app)

### What happened?

The Ubuntu WSL environment can be registered and `copilotd` starts successfully. Creating a new worktree session for a project in that environment then fails with:

```text
Failed to create session: invalid argument: rpc error -32603: internal error: could not verify GitHub identity
```

The failure occurs during `authenticate_host`. It subsequently causes protected operations to fail with:

```text
rpc error -32007: authentication required for https://api.github.com
```

The app health check reports that GitHub authorization for `github.com` is valid. WSL can reach `https://api.github.com` successfully, and no HTTP, HTTPS, or ALL proxy variables are configured.

### Steps to reproduce

1. Install or update the Windows app to v1.1.14.
2. Enable the `WSL hosts (Preview)` experimental feature and restart the app.
3. Add the Ubuntu WSL environment under Settings > Environments.
4. Add or select a project located in that WSL environment.
5. Attempt to create a new worktree session.
6. Observe that session creation fails while verifying the GitHub identity.

### Expected behavior

The app should pass or establish its authenticated GitHub identity with the WSL host, allowing the worktree session to be created.

### Additional context

Sanitized sequence from the application log:

```text
INFO spawning wsl copilotd (direct exec, no shell) distro="Ubuntu" executable=/.local/bin/copilotd
INFO adopted the daemon's endpoint record from its own stdout distro="Ubuntu" listen= daemon_pid= version=0.7.3 keys=4
INFO wsl rehydrate complete env_id=wsl:Ubuntu new_url=
WARN authenticate_host: transport error host_id=wsl:Ubuntu error=rpc error -32603: internal error: could not verify GitHub identity
WARN host authentication failed; protected resource calls may fail workspace_id= project_id= host_id=wsl:Ubuntu error=invalid argument: rpc error -32603: internal error: could not verify GitHub identity
WARN createResourceWatch failed workspace_id= project_id= host_id=wsl:Ubuntu uri= error=rpc error -32007: authentication required for https://api.github.com
WARN run_git: attempt 1 failed before dispatch; recreating shell and retrying host_id=wsl:Ubuntu error=git error on host `wsl:Ubuntu`: createTerminal for run_git shell failed: rpc error -32007: authentication required for https://api.github.com
ERROR failed to create session error=invalid argument: rpc error -32603: internal error: could not verify GitHub identity
```

Health-check observations:

- App authorization status: `ok` (`GitHub authorization is valid.`)
- Bundled Copilot CLI: 1.0.80, found successfully
- Pinned and running `copilotd`: 0.7.3
- WSL daemon startup and rehydration complete before authentication fails
- GitHub API root request from WSL returns HTTP 200
- Unauthenticated `/user` request returns HTTP 401 as expected

This appears related to #3216, which reports the same downstream `authentication required for https://api.github.com` error on v1.1.14. This report differs because WSL registration and daemon startup complete; the failure occurs specifically when creating a session and verifying the app's GitHub identity.

I have not attached the full diagnostics archive because it contains private local paths and repository metadata. I can provide it through a private channel if needed.