"Pending message" doesn't clear on correct timming

### Describe the bug

Found an issue where my Pending message is already consumed and the agent is thinking on it (I can read the thinking) but the message still has "(pending)" appended to it, thus misleading me.

### Affected version

GitHub Copilot CLI 1.0.75.

### Steps to reproduce the behavior

1. Ask tasks that need thinking while on medium or high thinking
2. Add additional prompts while it is still processing (you message is now pending)
3. Check the "Pending message" is appended
4. when the agent start thinking about your message, check the "Pending message" text is still present, although the message has already been delivered.

### Expected behavior

The "pending message" should clear before the agent starts thinking about the message, becaue by now it no longer is pending but was already delivered.

### Additional context

_No response_

Reproduce this in GitHub Copilot CLI 1.0.75 by sending a queued prompt during medium or high thinking, then observe it when the agent begins processing that prompt. Trace the pending-message display through the transition from queued to delivered, and consider the issue done when the “(pending)” text disappears before the agent starts thinking about the message.

Written by the indexing model from the issue text.