argument-hint format validation issue

[wangvisual]

Describe the bug

The skills now failed to load with:
✖ .../SKILL.md: argument-hint must be a string

This is my setting:
argument-hint: [regression directory]

And from both vscode and claude spec:
https://code.visualstudio.com/docs/agent-customization/agent-skills

argument-hint	No	Hint text shown in the chat input field when the skill is invoked as a slash command. Helps users understand what additional information to provide (for example, [test file] [options]).

https://code.claude.com/docs/en/skills

argument-hint	No	Hint shown during autocomplete to indicate expected arguments. Example: [issue-number] or [filename] [format].

Affected version

GitHub Copilot CLI 1.0.65.

Steps to reproduce the behavior

Add this to SKILL.md frontmatter:
argument-hint: [regression directory]

Expected behavior

Success to load the skill

Additional context

Linux x64

[wangvisual]

Checked argument-hint for public skills, seems it's a string. So it might be better to either change the spec.
As this is mostly an option, that's why the spec using [], but if it's should be a string, the spec better to mention that it's in string format