Support Frontmatter for Rule Files

[adamhill]

Idea

Supporting frontmatter for applying rules to files explicitly / implicitly included in the context or returned by codesearch as inclusion targets would be useful as rule systems become more numerous and specialized.

• Uses simple fileglob syntax, directories are supported too
• Copilot and Cursor use this mechanism to good effect

Example:

---
description: '.NET MAUI component and application patterns'
applyTo: '**/*.xaml, **/*.cs'
---
<rules in MD>

Edit: @Juice10 just poked my brain and made me think:

• We could also add a
  languageDocs: @http://<language-docs>
  to trigger latest spec retrieval when needed

Challenges

• Possible onflict between -{mode} rules and what a frontmatter fileglob says
• Combinatorial testing for fileglob pattern combos

[Triquetra]

Great idea. continue.dev was in the process of moving all its config files to this format when I moved over to Kilo Code.