test: add skills catalog loading and validation tests

[Ayush7614]

Summary

Adds unit tests for strix.skills — previously untested despite growing community skill contributions.

Covers:

• Internal categories (scan_modes, coordination) excluded from user-selectable skills
• Regression guard for merged community skills (oauth, aws, django, prototype_pollution, insecure_deserialization)
• validate_requested_skills() success and error paths
• load_skills() frontmatter stripping, category-prefixed names, missing-skill handling
• Catalog integrity: every user-selectable skill loads non-empty content

Why

• Skills are markdown-only contributions with no runtime tests today
• Prevents broken frontmatter, missing files, or loader regressions from merging unnoticed
• No overlap with open PR test: cover report helpers _parse_dedupe_response and litellm routing predicates #597 (report dedupe/usage helpers)

Verification

uv run pytest tests/test_skills.py -v

Test plan

• pytest tests/test_skills.py — 11 passed locally
• ruff check tests/test_skills.py — clean

[greptile-apps]

Greptile Summary

This PR adds tests for the skills catalog loader and validator. The main changes are:

• Coverage for excluding internal skill categories.
• Regression checks for merged community skills.
• Validation tests for accepted, too many, and unknown skill names.
• Loader tests for frontmatter stripping, category prefixes, missing skills, and catalog content.

Confidence Score: 5/5

The changed tests look safe to merge after a small cleanup to the catalog content assertion.

• The imports and API expectations match the current skills loader.
• The new checks cover the main catalog and validation paths.
• The only issue found is an arbitrary content-length threshold that can reject valid short skills.

tests/test_skills.py

Important Files Changed

Filename	Overview
tests/test_skills.py	Adds skills catalog tests; one catalog integrity assertion is stricter than the loader contract it is checking.

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
tests/test_skills.py:87
**Short Skills Fail Catalog Test**

When a valid skill has non-empty content of 100 characters or less after frontmatter stripping, this catalog test fails even though the loader contract is satisfied. That can block lightweight skill additions for test policy rather than a broken catalog entry.

```suggestion
        assert content[name].strip(), f"{name}: loaded body is empty"
```

_{Reviews (1): Last reviewed commit: "test: add skills catalog loading and val..." | Re-trigger Greptile}

[greptile-apps]

Short Skills Fail Catalog Test

When a valid skill has non-empty content of 100 characters or less after frontmatter stripping, this catalog test fails even though the loader contract is satisfied. That can block lightweight skill additions for test policy rather than a broken catalog entry.

Suggested change

	assert len(content[name].strip()) > 100, f"{name}: loaded body too short"
	assert content[name].strip(), f"{name}: loaded body is empty"

Prompt To Fix With AI

This is a comment left during a code review.
Path: tests/test_skills.py
Line: 87

Comment:
**Short Skills Fail Catalog Test**

When a valid skill has non-empty content of 100 characters or less after frontmatter stripping, this catalog test fails even though the loader contract is satisfied. That can block lightweight skill additions for test policy rather than a broken catalog entry.

```suggestion
        assert content[name].strip(), f"{name}: loaded body is empty"
```

How can I resolve this? If you propose a fix, please make it concise.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

[Ayush7614]

cc: @rajpratham1