[BUG] CLI crashes and restarts when spinning multiple explore agents

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When i try to run my custom command:

"Please get extremely familiar with $ARGUMENTS using multiple explore agents in parallel. You must get familiar with it as if you made it and wrote the code yourself. You must ultrathink to know how many agents will be needed to reach that level of knowledge. Once you are receive the results from the agents, and assimilate it, show me in a short paragraph a distilled overview of it that displays your in-depth understanding of it.

You must make sure to tell the agents to return the result to you as an output and not try to write an .md file. This is important."

The best way i can describe it, is that claude code closes and reopens after throwing this error:
"This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason:
Error: No assistant message found
at Dd (file:///C:/Users/Morde/AppData/Roaming/npm/node_modules/@anthropic-ai/claude-code/cli.js:3356:12905)
at process.processTicksAndRejections (node:internal/process/task_queues:105:5)"

I do have to say that after that error message, it does proceed to run the 5 agents but the entire cli ui restarts before that happens. it looks very funky. I will attach a screenshot.

<img width="1713" height="910" alt="Image" src="https://github.com/user-attachments/assets/9a224730-5904-48ca-9acd-60e0663dff95" />

What Should Happen?

It should have just run the explore agents

Error Messages/Logs

This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason:
Error: No assistant message found
    at Dd (file:///C:/Users/Morde/AppData/Roaming/npm/node_modules/@anthropic-ai/claude-code/cli.js:3356:12905)
    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)

Steps to Reproduce

Just make a custom command with:

"Please get extremely familiar with $ARGUMENTS using multiple explore agents in parallel. You must get familiar with it as if you made it and wrote the code yourself. You must ultrathink to know how many agents will be needed to reach that level of knowledge. Once you are receive the results from the agents, and assimilate it, show me in a short paragraph a distilled overview of it that displays your in-depth understanding of it.

You must make sure to tell the agents to return the result to you as an output and not try to write an .md file. This is important."

and run it with an arg.

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.25

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

<img width="1713" height="910" alt="Image" src="https://github.com/user-attachments/assets/fdf7b026-cd09-424b-b918-e491804b83ff" />