[BUG] Claude Code now unable to orchestrate multi-level agent trees

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?

The tool runtime has changed between 2.1.140 and 2.1.146, and subagents have lost the ability to spawn children by default unless the parent remembers to give very specific instructions. In Claude's own words:

The orchestrator wrote BLOCKED.md claiming "this harness has no Task / subagent dispatch tool" and proceeded serially. That's wrong — the Agent tool exists but is deferred; the orchestrator needed to ToolSearch for it first. My initial brief didn't make that explicit. So instead of W1-W9 in parallel across Sonnet subagents, you got one Opus working serially for ~27 minutes.

What Should Happen?

Child subagents should be able to launch descendants without the parent having to provide detailed operational instructions on the mechanics.

Error Messages/Logs

Steps to Reproduce

Ask Opus to launch another Opus to orchestrate a multi-step buildout regulating model and effort for subagents.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.140

Claude Code Version

2.1.146

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

_No response_