[BUG] "Claude Code on the web," subagents silently fail with 403/timeout errors and the parent agent doesn't surface the failure

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?

I was running two sessions of Claude code on the web on two different projects and using two different envs. One of the sessions failed silently and the parent agent didn't surface it until I prompt it and asked what is happening and then the parent agent restarted the task.
It happened to me twice (once today and once last week)

What Should Happen?

The parent agent should notice the crash and restart the task or notify the user

Error Messages/Logs

Steps to Reproduce

I was running two separate remote sessions, it is not happening every time...

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.42

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

PowerShell

Additional Information

Please note, it was Claude code on the web (remote env) and not local env