[BUG]

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?

• Version: 2.1.15
• Platform: Windows 11
• Issue: CLI hangs at "0 tokens" after background Task agents complete successfully
• Repro: Spawn 6-8 agents with run_in_background: true, agents complete, CLI freezes
• Related issues: #19195 (queue desync), #16590 (statsig), #19060 (no messages returned)
• Workarounds tried: Blocked statsig.anthropic.com and sentry.io, set DISABLE_TELEMETRY=1 - still hangs

This is clearly a CLI bug in how it handles agent completion notifications. The agents work fine, results come back,
but the main thread gets stuck waiting for something that already happened.

What Should Happen?

CLI should return to prompt after agents complete and allow continued interaction.

Actual Behavior

CLI hangs indefinitely showing "0 tokens" with no recovery. Agents complete successfully but the main thread never
resumes.

Error Messages/Logs

CLI hangs indefinitely showing "0 tokens" with no recovery. Agents complete successfully but the main thread never
  resumes.

Steps to Reproduce

• Issue is intermittent but frequent with 6+ concurrent background agents
• Single agents work fine
• Agents themselves complete successfully - only the CLI notification/resumption fails

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.15

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

<img width="1103" height="278" alt="Image" src="https://github.com/user-attachments/assets/e854cc08-7718-4b34-9d5c-5acf64fd4f6b" />