[Bug] GPT-5.6 Terra fails in Ask Mode

Environment

• OS: Windows 11 Enterprise Version: 25H2 Build: 26200.8875 Resource Pack: 1000.26100.334.0 Language: PT-BR
• Eclipse Version: 2026-06 (4.40.0) (Build id: 20260604-0653)
• Plugin Version: 0.21.0.202608060743

Describe the bug
GPT-5.6 Terra fails in Ask Mode with reasoning set to None: plugin still sends incompatible tools/reasoning via /v1/chat/completions

To Reproduce
Steps to reproduce the behavior:

1. Open a new Chat
2. Set the Agent Mode to 'Ask'
3. Set the model to GPT 5.6 - Terra
4. While setting the model, hover over your model choice to show the Thinking Effort menu.
5. Choose "None"
6. Write some basic prompt like "Explain the difference between an abstract class and an interface in Java"
7. See the error.

Expected behavior
Sorry, an error occurred while generating a response. Details: unhandled status from server: 400 { "error": { "message": "Function tools with reasoning_effort are not supported for gpt-5.6-terra in /v1/chat/completions. To use function tools, use /v1/responses or set reasoning_effort to 'none'.", "ty... Read more from logs.

Start by tracing the Ask Mode request path for GPT-5.6 Terra, focusing on how it selects /v1/chat/completions and includes tools or reasoning_effort when reasoning is set to None. Reproduce the issue with the listed steps, then verify that the request no longer triggers the reported 400 response.