Creating sub-agent hangs on MCP startup

What version of Codex CLI is running?

0.125.0

What subscription do you have?

plus

Which model were you using?

gpt-5.5

What platform is your computer?

win10 x64

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

Windows Terminal PowerShell7

What issue are you seeing?

Today I updated codex to the latest version, but when the main agent creates sub-agents, the sub-agents get stuck during startup on MCP. Every time, the last MCP fails to load. I thought it was an issue with that particular MCP, so I removed it, but the problem persisted—it still gets stuck on the last MCP. This morning, when using the codex app, this issue did not occur; I encountered it while using the CLI.

What steps can reproduce the bug?

Let the main agent (gpt-5.5 xhigh) create sub-agents and specify specific models and levels of reasoning (I created a specified sub-agent configuration toml in the agents folder, specifying that this sub-agent uses gpt-5.4 high; I don't know if this has affected the phenomenon).

What is the expected behavior?

The sub-agent is stuck in the startup state, and the last MCP will remain in the loading state.

Additional information

_No response_