fix(skills): handle single-line descriptions in SKILL.md frontmatter

[saiteja00743]

Summary

Fix skill discovery silently failing when the description field in SKILL.md frontmatter is written on a single line (i.e., the closing --- marker immediately follows the description with no blank line). Affected skills were completely invisible in /skills list.

Details

The root cause was two-fold:

1. FRONTMATTER_REGEX did not account for UTF-8 BOMs (\uFEFF) at the start of files, or trailing whitespace on --- delimiter lines, causing the regex to fail to match valid frontmatter blocks.

2. parseSimpleFrontmatter (the fallback YAML parser) incorrectly split single-line descriptions when subsequent lines contained name: or description:. It also was not case-insensitive and required exact colon formatting.

Changes to skillLoader.ts:

• Updated FRONTMATTER_REGEX to strip UTF-8 BOMs and tolerate trailing spaces/tabs on --- lines.
• Refactored parseSimpleFrontmatter to be case-insensitive, support optional spaces before colons, and use a negative lookahead to prevent misidentifying value lines as new keys.
• Replaced an unsafe as Record<string, unknown> type assertion with a proper isRecord() type guard to satisfy @typescript-eslint/no-unsafe-type-assertion.

Changes to skillLoader.test.ts:

• Added 7 new regression tests covering: single-line descriptions, UTF-8 BOM presence, trailing spaces after delimiters, case-insensitive keys, optional spaces before colons, robust non-string value casting, and indented description edge cases.

Related Issues

Fixes #25693

How to Validate

1. Create a skill with a single-line description:

   ---
   name: my-test-skill
   description: A single-line description
   ---
   Skill body here.

2. Place it in ~/.gemini/skills/my-test-skill/SKILL.md
3. Run npm run build && npm run start
4. Inside the CLI, run /skills list
5. Expected: my-test-skill appears with its description
6. Before fix: The skill would be missing from the list entirely

Alternatively, run the unit tests:

npm test -w @google/gemini-cli-core -- src/skills/skillLoader.test.ts

All 21 tests should pass.

Pre-Merge Checklist

• Updated relevant documentation and README (if needed) — no docs changes required
• Added/updated tests (if needed) — 7 regression tests added
• Noted breaking changes (if any) — no breaking changes
• Validated on required platforms/methods:
  • MacOS
    • npm run
    • npx
    • Docker
    • Podman
    • Seatbelt
  • Windows
    • npm run
    • npx
    • Docker
  • Linux
    • npm run
    • npx
    • Docker

[github-actions]

📊 PR Size: size/M

• Lines changed: 169
• Additions: +158
• Deletions: -11
• Files changed: 2

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a bug where skills with single-line descriptions in their SKILL.md frontmatter were failing to load. By improving the regex and fallback parsing logic, the system is now more resilient to variations in formatting, encoding, and indentation, ensuring all valid skills are correctly discovered.

Highlights

• Frontmatter Parsing Robustness: Updated the frontmatter regex to support UTF-8 BOMs and tolerate trailing whitespace on delimiter lines, ensuring valid frontmatter is correctly identified.
• Fallback Parser Improvements: Refactored the simple frontmatter parser to be case-insensitive, support flexible colon spacing, and prevent incorrect swallowing of subsequent keys during multi-line description parsing.
• Type Safety: Replaced unsafe type assertions with a robust isRecord type guard and added explicit string casting for frontmatter values.
• Regression Testing: Added 7 new unit tests covering edge cases like single-line descriptions, BOMs, trailing spaces, and case-insensitive keys.

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[gemini-code-assist]

Code Review

This pull request enhances frontmatter parsing in skillLoader.ts by supporting UTF-8 BOM, trailing spaces, case-insensitive keys, and non-string YAML values. It also adds a safe isRecord type guard and prevents the fallback parser from swallowing subsequent keys. A comprehensive suite of unit tests has been added to verify these improvements. No review comments were provided, so there is no additional feedback.