fix(#1326): stop emitting Codex agents/openai.yaml sidecars; clean up stale ones (#1360)

* fix(#1326): stop emitting Codex agents/openai.yaml sidecars; clean up stale ones

Codex installs wrote an agents/openai.yaml sidecar under every managed gsd-*
skill dir. Recent Codex builds index both SKILL.md and the sidecar, so each
GSD skill appeared twice in autocomplete (canonical gsd-* name + humanized
display_name).

- Replace writeCodexSkillMetadataFiles / generateCodexSkillMetadataYaml with
  cleanupCodexSkillMetadataSidecars: Codex-only (if isCodex), removes stale
  managed gsd-*/agents/openai.yaml and prunes the now-empty agents/ dir.
- Preserve user-owned dirs (gsd-dev-preferences), non-empty agents/ dirs, and
  non-gsd dirs; lstat-guard against symlinked agents/ so a delete can never
  escape the skills tree; fail-open per directory.
- Codex relies on SKILL.md alone for /skills discovery.
- Update USER-GUIDE/FEATURES docs and rewrite the #774 emission tests into
  cleanup tests.

Scope: the sidecar duplicate only. The separate multi-root (~/.agents/skills
shared-skills) duplicate facet is a distinct concern, not addressed here.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* chore(#1326): add changeset for Codex sidecar cleanup

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

docs/FEATURES.md

@@ -1053,7 +1053,7 @@ fix(03-01): correct auth token expiry
 - **Copilot:** `sessionStart`
 
 **Runtime-specific enrichments (1.4.0):**
-- Codex emits `service_tier: flex` for light-tier agents and an `agents/openai.yaml` chip so GSD skills appear in the Codex `/skills` picker
+- Codex emits `service_tier: flex` for light-tier agents; GSD skills appear in the Codex `/skills` picker via `SKILL.md` (no `agents/openai.yaml` sidecar is emitted — doing so caused duplicate autocomplete entries, #1326)
 - Gemini commands use native `{{args}}` interpolation
 
 **Native packaging:**