Fast mode toggle doesn’t take effect after switching off

What version of Codex CLI is running?

0.1180.

What subscription do you have?

plus

Which model were you using?

gpt-5.4 high

What platform is your computer?

windows

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

powershell

What issue are you seeing?

设置fast模式之后 如果/fast 关闭fast 无效，必须得重启才行
监测请求发现如果一开始设置了关闭fast 打开codex cli 是正常的，一旦切换到 fast on 之后 在切换回去 请求头中依然带有service_tier: "priority" 参数，导致fast不能热生效必须重启

What steps can reproduce the bug?

启动 codex cli 之前 设置 # service_tier = "fast" 为不开启
启动之后 /fast 设置 fast on
请求一次后 再次设置 /fast off
请求依然带有 service_tier: "priority"

What is the expected behavior?

预期是解决 /fast on 切换 off 不生效的问题

Additional information

_No response_