[Desktop] MCP tool calls fail with local models while the same MCP works with GPT-5.6

What version of the Codex App are you using (From “About Codex” dialog)?

26.810.41047

What subscription do you have?

free tier, i use ollama for work

What platform is your computer?

Darwin 25.4.0 arm64 arm

What issue are you seeing?

Description

I am experiencing an MCP tool-calling issue when using a local model in the Codex Desktop app.
The MCP server is discovered correctly and all of its tools are visible in the tool list, but calling an MCP tool with the local model fails with:
unsupported call
the exact same MCP configuration works correctly when I switch to GPT-5.6.

Environment

• OS: macOS
• Codex Desktop: 26.810.41047
• Local model: Qwen3.6-35B-A3B、ornith 35B-A3B
• MCP server: Brave Search MCP
• Provider: local/ollama

Important

Using the exact same Codex Desktop installation, MCP server, API key, and MCP configuration:

• GPT-5.6 + Brave Search MCP → works
• Qwen3.6-35B-A3B + Brave Search MCP → unsupported call

This suggests that the MCP server and API key are working correctly, and that the issue is specific to MCP tool invocation with the local/custom model provider.

What steps can reproduce the bug?

1. Configure the Brave Search MCP server in Codex.
2. Start Codex Desktop.
3. Use Qwen3.6-35B-A3B as the model.
4. Ask the model to perform a web search using the Brave MCP tool.
5. The MCP tool is visible in the available tools, but the invocation fails with:

unsupported call

What is the expected behavior?

MCP tools should be callable when using a compatible local/ollama provider, just as they are when using GPT-5.6.

Additional information

This appears to be related to the existing issues concerning MCP namespace tools and non-OpenAI/custom model providers.

However, I am reporting this separately because my reproduction is specifically on the Codex Desktop app, not the Codex CLI.

I hope this helps distinguish the Desktop reproduction from the CLI-related reports.