Wrong model billed

### Describe the bug

When I prompted Copilot using auto model selection, it informed me that it used GPT-5.3-Codex in chat window:

But when done, it reported GPT-5.4:

Also when I opened my usage page in GitHub account settings, I saw GPT-5.4 as the only "Auto" model usage:

The thing is that the response style seemed to be that of GPT-5.3-Codex and I've been charged for GPT-5.4

### Affected version

VSCode Insiders extension - GitHub Copilot Chat v0.56.2026070103

### Steps to reproduce the behavior

1. Select "auto" model selection
2. Send prompt
3. Observe initial information on selected model
4. Observe response style
5. Observe summary information on model used
6. Observe AI usage billing chart in account settings

### Expected behavior

Initial selected model info, summary model info, actually used model and billing info should all be unanimous

### Additional context

_No response_

No source file, test, or entry point is named. Start by reproducing the steps with auto model selection and compare the initial model label, response summary, and account usage chart; the issue is done when these consistently identify the actually used model and billing information agrees.

索引モデルが issue の本文から書いたものです。