excludeAgent does not work on subagents

[inprealpha]

Describe the bug

As of right now, excludeAgent in the frontmatter block does not work on subagents.

This limits custom instructions which are meant for main agent but not subagents.

Affected version

GitHub Copilot CLI 1.0.10

Steps to reproduce the behavior

1. Set up custom instructions with excludeAgent
2. Test if subagents are following custom instructions

Expected behavior

excludeAgent in the frontmatter block would extend to subagents.

Additional context

No response