Subagents sometimes spawned with service_tier=priority

What version of Codex CLI is running?

0.142.0

What subscription do you have?

Pro 20x

Which model were you using?

gpt-5.4

What platform is your computer?

Linux 6.18.33.1-microsoft-standard-WSL2 x86_64 x86_64

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

Windows Terminal

Codex doctor report

What issue are you seeing?

I usually have Fast Mode turned off and its also the default in config.toml.

However, in one session I saw that the main agent spawned a subagent with FastMode=On. I asked how this could have happened and it turns out there is a service_tier=priority mode that can be used during spawning subagents.

This is a critical issue as it undermines the global policy, the setting for the main agent and silently swallows tokens for breakfast.

What steps can reproduce the bug?

The main agent randomly selects whether the subagent should be spawned with Fast Mode or not - I can not reliably reproduce it.

What is the expected behavior?

Spawned subagents should receive the same service tier as the main agent by default.

Additional information

_No response_