Claude Opus 4.5 requests return error 400

**Describe the bug**
When making an Agent request using Claude Opus 4.5 I have been getting the same error message all day:

Sorry, an error occurred while generating a response. Details: unhandled status from server: 400 {"error": {"message": "messages.1.content.0.thinking: each thinking block must contain thinking","code":"invalid_request_body"}} Request ID: xxx

**Versions**
- Copilot for Xcode: 0.46.0
- Xcode: 26.2.0
- macOS: 26.2

**Steps to reproduce**
1. Select Claude Opus 4.5 as model
2. Select Agent mode
3. Enter prompt
4. Error is returned

**Screenshots**

**Logs**
[github-copilot-for-xcode.log](https://github.com/user-attachments/files/24520525/github-copilot-for-xcode.log)

**Additional context**
Attempted the following to try and resolve:
- Signing out then back in
- Cleaning DerivedData/Copilot cache
- Restarting device
- Uninstalling / Reinstalling Copilot