[BUG] Copilot Chat integration fails — Claude Copilot Proxy rejects model "claude-opus-4.6" as not supported

Bug description

The Claude Code extension's Copilot Chat integration (Claude Copilot Proxy) rejects requests from Copilot Chat with 400 model_not_supported. Copilot Chat sends model name claude-opus-4.6 but the proxy doesn't recognize it.

Reproduction steps

1. Have Claude Code extension and GitHub Copilot Chat extension installed
2. Open Copilot Chat and select a Claude model
3. Send any message
4. Get "Error during execution"

Error logs (from Copilot Chat output)

[ClaudeLanguageModelServer] Claude Language Model Server started on http://localhost:2573
Server error: 400 {"error":{"message":"The requested model is not supported.","code":"model_not_supported","param":"model","type":"invalid_request_error"}}
ccreq:69a27063.copilotmd | failed | claude-opus-4.6 | 282ms | [Claude Copilot Proxy]

Retried 3 times, same error each time.

Environment

• OS: Windows 11 Pro (10.0.26200)
• VS Code: 1.110.1
• Claude Code extension: 2.1.71
• GitHub Copilot Chat: 0.38.2

Notes

The Claude Code native chat panel works fine. Only the Copilot Chat integration via the Claude Copilot Proxy is broken. The issue appears to be a model name mapping problem — the proxy doesn't map claude-opus-4.6 to a valid API model ID.