[BUG] .mdc files excluded from @ imports in CLAUDE.md since v2.1.2

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Since v2.1.2, .mdc files (Cursor rule files) are no longer imported via @ syntax in CLAUDE.md. It appears that the binary file exclusion logic introduced in v2.1.2 is also excluding .mdc files.

In v2.1.1, .mdc files were correctly imported and included in the memory files.

What Should Happen?

.mdc files should be imported via @ syntax in CLAUDE.md since v2.1.2, as they are plain text files (Markdown-like) and not binary files.

This is especially important for users who use both Cursor and Claude Code in parallel, as they can share rule files between the two tools.

Related: https://github.com/anthropics/claude-code/releases/tag/v2.1.2

Error Messages/Logs

No error messages. The .mdc file is silently excluded from the import.

Steps to Reproduce

1. Clone the reproduction repository: https://github.com/ichizero/claude-mdc-imports-repro
2. Start Claude Code in the repository
3. Run /context command to check memory files
4. Notice that @.cursor/rules/sample-cursor-instructions.mdc is not imported (only docs/sample-instructions.md is shown)

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.1

Claude Code Version

2.1.9

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

I understand that Claude Code has its own modular rules system, .claude/rules. However, being able to import .mdc files was useful for users who work with both Cursor and Claude Code, allowing them to share instructions between the two tools.

Would it be possible to restore the previous behavior where .mdc files were treated as text files and imported correctly?

Reproduction repository: https://github.com/ichizero/claude-mdc-imports-repro