fix: use block-style YAML sequences in SKILL.md frontmatter

[ademakdogan]

Description

Replace flow sequences (bins: ["gws"], skills: [...]) with block-style sequences in all generated SKILL.md frontmatter templates.
Flow sequences are valid YAML but rejected by strictyaml, which the Agent Skills reference implementation (agentskills validate) uses to parse frontmatter. This caused all 93 generated skills to fail validation.
Also adds unit tests verifying that service, shared, persona, and recipe skill templates produce block-style sequences only.
Fixes #521
Dry Run Output:

N/A

Checklist:

• My code follows the AGENTS.md guidelines (no generated google-* crates).
• I have run cargo fmt --all to format the code perfectly.
• I have run cargo clippy -- -D warnings and resolved all warnings.
• I have added tests that prove my fix is effective or that my feature works.
• I have provided a Changeset file (e.g. via pnpx changeset) to document my changes.

[changeset-bot]

🦋 Changeset detected

Latest commit: 923a1d6

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@googleworkspace/cli	Patch

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[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 refactors the YAML output for skill frontmatter to comply with stricter parsing rules, specifically those enforced by strictyaml. By switching from flow sequences to block-style sequences, the change ensures that all generated skill definitions are correctly validated, thereby improving the robustness and compatibility of the skill generation process. The update also includes new tests to prevent regressions in YAML formatting.

Highlights

• YAML Frontmatter Formatting: Updated the generation of SKILL.md frontmatter templates to use block-style YAML sequences instead of flow sequences. This change addresses an incompatibility with strictyaml, which rejected the previous flow-style format.
• Validation Fix: Resolved an issue where all 93 generated skills failed validation due to strictyaml's strict parsing of YAML sequences, ensuring all skills now pass validation.
• Unit Testing: Added comprehensive unit tests to verify that service, shared, persona, and recipe skill templates consistently produce block-style YAML sequences in their frontmatter.

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[gemini-code-assist]

Code Review

This pull request correctly replaces YAML flow sequences with block-style sequences in the generated SKILL.md frontmatter to ensure compatibility with strictyaml. The changes are applied consistently across service, shared, persona, and recipe skill templates. The addition of unit tests to verify the output format is a great improvement that will prevent regressions. I have one suggestion regarding the new test assertions to make them more robust against future changes.

[googleworkspace-bot]

/gemini review

[gemini-code-assist]

Code Review

This pull request correctly resolves the YAML validation issue by converting flow-style sequences to block-style sequences in the generated SKILL.md frontmatter. The changes are applied consistently across all relevant skill generation functions. The addition of a comprehensive set of unit tests is a significant improvement that ensures the generated YAML remains compliant and prevents future regressions. The code is clean, focused, and effectively addresses the problem.