## Summary
- Fixes syntax highlighting issue where Rust hex literals with
underscores after hex letters (like `0x01_02_0a_0b`) would lose
highlighting after the underscore
- Created custom Rust language mode (`rustp`) that patches Monaco's
built-in tokenizer
- Filed upstream issue with Monaco Editor:
https://github.com/microsoft/monaco-editor/issues/4917
## Test plan
- [x] Verified fix works locally with test cases like `0x01_02_0a_0b`,
`0xFF_AA_BB_CC`, etc.
- [x] Confirmed all existing tests pass
- [x] Checked that TypeScript compilation and linting pass
🤖 Generated with [Claude Code](https://claude.ai/code)
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Co-authored-by: Claude <noreply@anthropic.com>
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