BYOK CustomEndpoint Model only thinks, cannot parse or strip `delta.reasoning`

• Copilot Chat Extension Version: GitHub.copilot-chat 0.41
• VS Code Version: 1.126.0
• OS Version: Win 11
• Feature (e.g. agent/edit/ask mode): all responses
• Selected model (e.g. GPT 4.1, Claude 3.7 Sonnet): CustomEndpoint (Qwen3-VL-235B-A22B-Thinking-FP8)

Steps to Reproduce:

1. Assign a reasoning model as a custom endpoint.
2. Ask it to do or say anything.
3. Click on the "Finished in.." section when you receive the error to see the thinking.

This does not happen with qwen3.6-27b, which can "think" and "respond" as normal. It seems to be that the extension does not expect and cannot handle delta.reasoning. Here is a partial raw response to a "Hello" outside of GHCchat:

curl ... '{"model":"billiken-coder-prodigy","messages":[{"role":"user","content":"Hello"}],"stream":true}'
data: {"id":"chatcmpl-be7c326e84b87a6e","object":"chat.completion.chunk","created":1782492920,"model":"billiken-coder-prodigy","choices":[{"index":0,"delta":{"role":"assistant","content":""},"logprobs":null,"finish_reason":null}],"prompt_token_ids":null,"prompt_text":null}

data: {"id":"chatcmpl-be7c326e84b87a6e","object":"chat.completion.chunk","created":1782492920,"model":"billiken-coder-prodigy","choices":[{"index":0,"delta":{"reasoning":"Okay"},"logprobs":null,"finish_reason":null,"token_ids":null}]}

data: {"id":"chatcmpl-be7c326e84b87a6e","object":"chat.completion.chunk","created":1782492920,"model":"billiken-coder-prodigy","choices":[{"index":0,"delta":{"reasoning":","},"logprobs":null,"finish_reason":null,"token_ids":null}]}

data: {"id":"chatcmpl-be7c326e84b87a6e","object":"chat.completion.chunk","created":1782492920,"model":"billiken-coder-prodigy","choices":[{"index":0,"delta":{"reasoning":" the"},"logprobs":null,"finish_reason":null,"token_ids":null}]}

data: {"id":"chatcmpl-be7c326e84b87a6e","object":"chat.completion.chunk","created":1782492920,"model":"billiken-coder-prodigy","choices":[{"index":0,"delta":{"reasoning":" user"},"logprobs":null,"finish_reason":null,"token_ids":null}]}

data: {"id":"chatcmpl-be7c326e84b87a6e","object":"chat.completion.chunk","created":1782492920,"model":"billiken-coder-prodigy","choices":[{"index":0,"delta":{"reasoning":" said"},"logprobs":null,"finish_reason":null,"token_ids":null}]}

...

data: {"id":"chatcmpl-be7c326e84b87a6e","object":"chat.completion.chunk","created":1782492920,"model":"billiken-coder-prodigy","choices":[{"index":0,"delta":{"content":" 😊"},"logprobs":null,"finish_reason":null,"token_ids":null}]}

data: {"id":"chatcmpl-be7c326e84b87a6e","object":"chat.completion.chunk","created":1782492920,"model":"billiken-coder-prodigy","choices":[{"index":0,"delta":{},"logprobs":null,"finish_reason":"stop","stop_reason":null,"token_ids":null}],"system_fingerprint":"vllm-0.23.0-tp4-ep-68660ca4"}

data: [DONE]