Skills loader ignores symlinked SKILL.md files (breaks stow/dotfiles setups)

Summary

When skills are installed as symlinked SKILL.md files (common with dotfiles managers like GNU Stow), Codex does not discover/load them.

Symlinked directories are followed for user/admin/repo scopes, but symlinked SKILL.md files are explicitly skipped. This makes it hard to manage ~/.codex/skills via dotfiles without copying files.

Steps to reproduce

1. Create a skill file somewhere, e.g. /tmp/shared/demo/SKILL.md.
2. Create a user skill folder and symlink the SKILL.md into it:

• mkdir -p ~/.codex/skills/demo
• ln -s /tmp/shared/demo/SKILL.md ~/.codex/skills/demo/SKILL.md

1. Run Codex and list skills.

Expected behavior

The skill should be discovered/loaded (or at least there should be a clear error / documented limitation).

Actual behavior

No skill is loaded.

Code pointers

In codex-rs/core/src/skills/loader.rs, discover_skills_under_root checks entry.file_type().is_symlink() and only follows symlinks that resolve to directories; symlinks to files are skipped.

There is also an explicit test asserting this behavior: ignores_symlinked_skill_file_for_user_scope.

Why this matters

Tools like GNU Stow manage dotfiles by creating symlinks for the actual files, so ~/.codex/skills/**/SKILL.md ends up being symlinked. Today that means user skills silently disappear unless they’re copied into place as real files.

Possible fixes

• If follow_symlinks is true for user/admin/repo scopes, consider resolving symlinked SKILL.md files (and parsing the resolved path) instead of skipping them.
• Alternatively, document that only symlinked directories are supported (not symlinked SKILL.md files), and explain recommended dotfiles workflows.