fix(skills): follow symlinks during skill discovery (#35184)

[Tranquil-Flow]

What does this PR do?

Skill discovery (_find_skill in tools/skill_manager_tool.py) uses
Path.rglob() which does not follow symlinks into directories. Skills
stored under symlinked category directories were invisible to the agent.

Fix: Replace Path.rglob() with os.walk(followlinks=True) via the
existing iter_skill_index_files() helper in the same module.

Related Issue

Fixes #35184

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)

Changes Made

• tools/skill_manager_tool.py: Replace Path.rglob() call with
  iter_skill_index_files() (which uses os.walk(followlinks=True))
  for symlink-aware directory traversal.
• tests/tools/test_skill_symlink_discovery.py: New — regression
  test that creates a symlinked category directory and verifies skills
  under it are discovered.

How to Test

1. Run python3 -m pytest tests/tools/test_skill_symlink_discovery.py -v
2. Verify skills in symlinked directories are found

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features)

[alpindiay]

Automated Triage: Competing PRs Detected

Three PRs are independently fixing the same issue (symlink-discovery in skills, #35184):

• fix(skills): follow symlinks during skill discovery (#35184) #35213 (this PR)
• fix(skill_manager): follow symlinks when discovering skills (#35184) #35244
• fix: rglob follow symlinks for skill discovery #35299

They all modify tools/skill_management.py — only one can merge cleanly. Please coordinate and consolidate into a single PR.

[teknium1]

Thanks for targeting a confirmed residual skill-discovery path. Current main still uses rglob("SKILL.md") in tools/skill_manager_tool.py:597 and tools/skill_manager_tool.py:661, while agent/skill_utils.py:796 already provides the intended symlink-following traversal.

Problems

• tests/tools/test_skill_symlink_discovery.py:42 calls os.symlink without handling unavailable symlink privileges. Existing tests skip cleanly on OSError/NotImplementedError in tests/tools/test_skills_tool.py:47-55.
• iter_skill_index_files() follows links at agent/skill_utils.py:796 but has no visible cycle guard. A cyclic directory link could make the newly migrated management lookups non-terminating.
• The same direct lookup pattern remains in tools/skill_usage.py:841 and tools/skill_usage.py:858; assess whether those curator/usage paths should share the iterator too.

Suggested changes

• Make the regression test skip when symlink creation is unavailable.
• Add cycle protection in the shared iterator and cover it with a regression test before extending its use.

Automated hermes-sweeper review.

[teknium1]

Please handle OSError and NotImplementedError here and skip when symlinks are unavailable. The established helper in tests/tools/test_skills_tool.py:47-55 keeps these tests portable to restricted Windows environments.