[Bug] it currently defaults to use "fast" mode in gpt 5.5 subagent .

What version of Codex CLI is running?

0.142.3

What subscription do you have?

When using subagent to call the GPT 5.5 model within a GPT 5.4 session, it currently defaults to use "fast" mode in gpt 5.5 subagent .

Which model were you using?

GPT 5.4

What platform is your computer?

macos

What terminal emulator and version are you using (if applicable)?

_No response_

Codex doctor report

What issue are you seeing?

1. in main session, GPT5.4
2. use prompt to handoff task to agent GPT5.5
3. it currently defaults to use "fast" mode in gpt 5.5 subagent . expect: not use fast mode

<img width="394" height="426" alt="Image" src="https://github.com/user-attachments/assets/4639bbc5-53ee-40fa-9aeb-ff337392f244" />
<img width="440" height="197" alt="Image" src="https://github.com/user-attachments/assets/b336b4f9-b1d6-47f4-8605-d8bd7c5991d2" />

What steps can reproduce the bug?

Uploaded thread: 019f0d6a-decd-7170-b4ce-218d0a5b0c8b

What is the expected behavior?

_No response_

Additional information

_No response_