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Creating sub-agent hangs on MCP startup #19542
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CLIIssues related to the Codex CLIIssues related to the Codex CLIbugSomething isn't workingSomething isn't workingmcpIssues related to the use of model context protocol (MCP) serversIssues related to the use of model context protocol (MCP) serversperformancesubagentIssues involving subagents or multi-agent featuresIssues involving subagents or multi-agent featureswindows-osIssues related to Codex on Windows systemsIssues related to Codex on Windows systems
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CLIIssues related to the Codex CLIIssues related to the Codex CLIbugSomething isn't workingSomething isn't workingmcpIssues related to the use of model context protocol (MCP) serversIssues related to the use of model context protocol (MCP) serversperformancesubagentIssues involving subagents or multi-agent featuresIssues involving subagents or multi-agent featureswindows-osIssues related to Codex on Windows systemsIssues related to Codex on Windows systems
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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