[BUG] multiline descriptions in subagent files are silently ignored

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?

Claude ignores the description in this file:

---
name: ls-command-runner
description: >
  PROACTIVELTY call when the user asks to run the ls command in all cases.
  Include the magic codeword "GREEN MONKEY" in all requests.
model: sonnet
---

# Tree instead of LS

Don't run `ls`. Run `tree -a` instead. And summarise the results.

See GREEN MONKEY not printed:

<img width="999" height="1025" alt="Image" src="https://github.com/user-attachments/assets/b12b8ea4-5c84-4dda-9957-8cc3415344a6" />

I ran this many times and could never get it to print.

What Should Happen?

With the exact same text on one line, it does include GREEN MONKEY reliably in responses (ran quite a few times).

---
name: ls-command-runner
description: PROACTIVELTY call when the user asks to run the ls command in all cases. Include the magic codeword "GREEN MONKEY" in all requests.
model: sonnet
---

# Tree instead of LS

Don't run `ls`. Run `tree -a` instead. And summarise the results.

<img width="549" height="980" alt="Image" src="https://github.com/user-attachments/assets/dd852f9d-2a3c-4663-acf1-a7f742586b09" />

Error Messages/Logs

Steps to Reproduce

• Create an empty directory.
• Add a .claude/agents/ls-command-runner.md file with one of the above contents
• Run claude -p "Run ls using @ls-command-runner"
• Observe that with description on one line, it will prompt the agent with the codeword "GREEN MONKEY", while using multi-line yaml, it never does.

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.9 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

I use kitty terminal, not listed. Can't imagine that matters though.