[BUG] SendMessage no longer available

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?

SendMessage appears in the system-available deferred tools list but is not present in the actual tool set when fetched. Reproducible across multiple session restarts on the same machine. Makes inter-agent communication impossible despite the tool appearing to be configured.

THIS IS A CRITICAL ISSUE AGENTS ARE FLYING BLIND.

This was working fine yesterday

What Should Happen?

SendMessage is not available to me. I can only communicate with background agents by launching a new agent. That's why earlier I had to spawn a separate "correction" agent instead of directly messaging the running Skeptic. Once an agent is running in the background, I have no way to reach it mid-execution.

Error Messages/Logs

SendMessage is not available to me. I can only communicate with background agents by launching a new agent. That's why earlier I had to spawn a separate "correction" agent instead of directly messaging the running Skeptic. Once an agent is running in the background, I have no way to reach it mid-execution.

Steps to Reproduce

Ask instance to run SendMessage to another agent

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude 1.569.0 (49894a) 2026-04-02T20:01:42.000Z

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_