fix: prevent empty descriptions from being serialized as YAML null in frontmatter

[r1bilski]

closes #1068

[cm-dyoshikawa]

/oc review

[github-actions]

All CI checks pass. Here's my review:

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PR #1070 Review: Fix empty descriptions serialized as YAML null

Summary

This PR fixes issue #1068 where empty descriptions were being serialized as YAML null in frontmatter, causing Zod validation errors since z.optional(z.string()) does not accept null.

Changes Analysis

Core Fix - src/utils/frontmatter.ts:67-73

• Added deepRemoveNullishObject() call in parseFrontmatter() to strip null/undefined values
• Ensures YAML bare keys like description: (which parse as null) are removed before Zod validation
• Consistent with existing stringifyFrontmatter() behavior

Downstream Updates

• rulesync-rule.ts:162 - Removed ?? "" fallback, now preserves undefined
• tool-rule.ts:177 - Same change for consistency
• cursor-rule.ts:92 - Changed !== undefined to truthy check to also skip empty strings

Test Coverage

Excellent coverage added:

• Null stripping in frontmatter.test.ts (top-level and nested)
• Cursor rule roundtrip tests verifying no description: in output
• Re-import tests for YAML null description files
• Existing tests updated to expect undefined

Verdict

Approved. The implementation is correct, well-tested, and all 3821 tests pass. The fix properly handles the YAML parsing quirk where bare keys produce null values.

github run