Support ignoring files in .github/agents/ from agent loading

[brettcurtis]

Feature Request

Problem

Any .md file placed inside .github/agents/ is loaded as a Copilot agent. There is no supported way to exclude a file (e.g. a README.md index) from being treated as an agent.

Currently:

• A file with no YAML frontmatter fails with: custom agent markdown frontmatter is malformed: missing or malformed YAML frontmatter
• A file with valid frontmatter is loaded as an agent (undesired for index/documentation files)
• Adding ignored: true to frontmatter produces a warning: unknown field ignored: ignored

Proposed Solution

Add support for an ignored (or similar) frontmatter field that tells the CLI to skip loading a file as an agent, without producing a warning. For example:

---
ignored: true
description: Index of available agents in this repository.
---

This would allow teams to keep a README.md or other documentation file alongside their agent definitions without it appearing in the agent browser (/agent).

Use Case

Keeping a human-readable index file (README.md) in .github/agents/ to document available agents, without that file itself appearing as a selectable agent.