fix(skills): report inaccessible skill directories to on_error - #7760

Link to Issue or Description of Change

1. Link to an existing issue:

• Closes: skills: inaccessible directories silently bypass on_error on Python 3.14/3.15 #7749

2. Or, if no issue exists, describe the change: n/a

Problem

In _list_skills_in_dir, skill_dir.is_dir() runs before the try block. If reading directory metadata fails (e.g. PermissionError), on Python 3.11-3.13 the exception escapes without on_error being called; on Python 3.14/3.15 Path.is_dir() returns False for any OSError, so the skill is silently dropped and on_error never fires.

Solution

Check the entry with skill_dir.stat() + stat.S_ISDIR() so OSError is not suppressed. FileNotFoundError/NotADirectoryError (dangling symlink, entry removed mid-listing) still count as "not a directory" and are skipped as before. Any other OSError goes through a small local report() helper shared with the existing per-skill failure path: it calls on_error(skill_id, error) if provided, otherwise logs the same warning. The rest of the loop is unchanged.

Out of scope: the other is_dir() uses in skills/_utils.py (_load_skill_from_dir, load_skills_from_dir, _validate_skill_dir, and the base-path check) are left as-is.

Testing Plan

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

New tests in tests/unittests/skills/test__utils.py patch pathlib.Path.stat for one child to raise PermissionError (not is_dir): on_error receives the name and exception while other skills still load; on_error can abort; no on_error logs a warning and continues; non-directory files and dangling symlinks are skipped without calling on_error.

PYTHONPATH=$PWD/src pytest tests/unittests/skills -q
129 passed

Before the fix (src stashed), 2 of the new tests fail with PermissionError escaping.

Manual End-to-End (E2E) Tests:
Reproduced on a real Python 3.14.7 interpreter with a skills directory that is listable but not searchable (chmod 0o444), so stat() of its children fails with PermissionError:

• Before the fix: _list_skills_in_dir(..., on_error=cb) returns {} and cb is never called (silent drop).
• After the fix: cb('blocked', PermissionError) and cb('good', PermissionError) are called.

The unit tests simulate the same failure at the Path.stat boundary so they run on any version and any OS.

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.