Handle incorrectly formatted front mater in `description` field in subagent config

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

My agent configs were defined like this:

---
name: ui-ux-designer
description:
  Create interface designs, wireframes, and design systems. Use PROACTIVELY for design systems, user flows, or interface
  optimization.
---

Because I am using Prettier for formatting Markdown file, and Prettier adds an end-line after the :.

My agents weren't recognized by Claude.

The issue was incorrect front matter. Markdown uses YAML for the front matter, and the description is turned into a mapping when there is an end-line after :.

The fix was to add a |:

+ description: |
- description:

Proposed Solution

Handle the error and bubble it up, informting the user their front matter configuration is incorrect so that they don't have to guess what's wrong.

Priority

Medium - Would be very helpful

Feature Category

Configuration and settings

Additional Context

Related: https://github.com/anthropics/claude-code/issues/4695