fix(skills): prevent frontmatter name from diverging from directory name

[akimuz]

Related Issue

Fixes #21782

What changed and why

skill_manage(action="create", name="foo", content="---\nname: bar\n...") silently
created a skill whose directory is foo/ but whose skills_list() display name is
bar. The write path never validated that the frontmatter name matches the name
parameter, introducing a dual-namespace problem:

• skills_list() shows the frontmatter name → bar
• skill_view("bar") → not found (directory-name lookup)
• skill_manage(action="edit", name="foo") → found (directory-name lookup)

Same divergence could be introduced via edit or patch.

Previous fixes (#17914, #18872, #5433, #7669) patched read-path symptoms
(skill_view can't resolve frontmatter name, bundled skill misclassified, etc.).
This PR fixes the write-path root cause: _validate_frontmatter() now accepts an
expected_name parameter and cross-checks it against the frontmatter name field.
All three write paths (_create_skill, _edit_skill, _patch_skill) wire the
directory name through so mismatches are explicitly rejected with an actionable
error message, rather than silently accepted.

Design choice: explicit rejection over silent auto-overwrite — the error message
lets the agent self-correct on the next turn.

How to test

Reproduction (without fix):

skill_manage(
    action="create",
    name="local-paper-summarizer",
    content="---\nname: local-paper-summary\ndescription: ...\n---\n\nSteps..."
)
# skills_list() shows "local-paper-summary"
# skill_view("local-paper-summary") → not found

With fix — mismatch rejected:
skill_manage(
    action="create",
    name="local-paper-summarizer",
    content="---\nname: local-paper-summary\ndescription: ...\n---\n\nSteps..."
)
# → "Frontmatter name 'local-paper-summary' does not match skill name
#    'local-paper-summarizer'. The frontmatter name must match the 'name' parameter."

Unit tests:
pytest tests/tools/test_skill_manager_tool.py -v

New test cases:
- create with frontmatter name ≠ name param → fail
- create with frontmatter name == name param → succeed
- edit changing frontmatter name away from directory name → fail
- patch altering name: to diverge from directory name → fail

Platforms tested

- macOS (Darwin 24.2.0, Python 3.11)

Related

- #17914 / #18872 — read-path: skill_view vs skills_list name mismatch
- #5433 — read-path: bundled manifest vs frontmatter name causes misclassification
- #7669 — read-path: _get_skill_type() vs _scan_skill_names() name mismatch

[alt-glitch]

Competing PR: #21806 addresses the same root cause (fixes #21782) with a broader scope (also touches whatsapp.py, file_tools.py). Both add expected_name validation to _validate_frontmatter(). Maintainers should pick one.

[akimuz]

Competing PR: #21806 addresses the same root cause (fixes #21782) with a broader scope (also touches whatsapp.py, file_tools.py). Both add expected_name validation to _validate_frontmatter(). Maintainers should pick one.
Thanks for the clarification
Since #21806 covers the same invariant and extends to more downstream paths, I'll close this PR now
Thanks again for the review