When adding two steering message the first gets queued which messes up order.

### Describe the bug

When steering, and then you have another idea and steer again, the order of the steering messages is flipped and the first message is queued. Leading to the wrong order of execution.

This happens a lot when you think of relevant context after firing off the steering message.

### Affected version

GitHub Copilot CLI 1.0.78. Run 'copilot update' to check for updates.

### Steps to reproduce the behavior

1. Start a task in copilot CLI
2. Give it a steering message
3. Before it's finished processing steer again, e.g. adding more context

This leads to the first steering message being queued, and the second steering message being used now, which would even be confusion for a human.

### Expected behavior

Steering happens in the order we steer, and is not queued without asking to queue.

### Additional context

- OS: MacOS
- Shell: Nushell
- Terminal: Ghostty (seems to have with normal Mac terminal as well though)

Start by reproducing the behavior in Copilot CLI 1.0.78: send one steering message, then another before processing finishes, using the steps in the issue. Trace the steering-message handling and queue entry point, then verify that steering messages execute in the order sent and are not queued without an explicit request.

Written by the indexing model from the issue text.