Copilot CLI resume session switches back to default model

### Describe the bug

bug: Copilot CLI resume session switches automatically back to default model

### Affected version

GitHub Copilot CLI 1.0.78.

### Steps to reproduce the behavior

## Steps to reproduce

1. Start a session with a specific model:

```bash
copilot --yolo --model=gpt-5.6-terra --reasoning-effort=high
```

2. Work in the session and exit Copilot CLI.

3. Resume the session:

```bash
copilot --resume
```

or:

```bash
copilot --model=gpt-5.6-terra --reasoning-effort=high --resume
```

After finishing loading the session , Copilot CLI silently switches to the default model before any human input.

The conversation context is restored correctly, but the selected model is not preserved.

## Expected behavior

The resumed session should continue using `gpt-5.6-terra` in the begining .

### Expected behavior

_No response_

### Additional context

_No response_

Reproduce the issue with GitHub Copilot CLI 1.0.78 using the listed --model, --reasoning-effort, and --resume commands. Trace how the resumed session restores its conversation and selected model; done means resuming a session keeps gpt-5.6-terra active before the next human input.

Written by the indexing model from the issue text.