fix: enforce Codex 1024-char description limit + auto-heal stale installs (v0.11.9.0) (#391)

* fix: enforce 1024-char Codex description limit + auto-heal stale installs

Build-time guard in gen-skill-docs.ts throws if any Codex description
exceeds 1024 chars. Setup always regenerates .agents/ to prevent stale
files. One-time migration in gstack-update-check deletes oversized
SKILL.md files so they get regenerated on next setup/upgrade.

* chore: bump version and changelog (v0.11.9.0)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

TODOS.md

@@ -489,6 +489,20 @@ Shipped in v0.8.3. Step 8.5 added to `/ship` — after creating the PR, `/ship`
 **Depends on:** gstack-diff-scope (shipped)
 
 
+## Codex
+
+### Codex→Claude reverse buddy check skill
+
+**What:** A Codex-native skill (`.agents/skills/gstack-claude/SKILL.md`) that runs `claude -p` to get an independent second opinion from Claude — the reverse of what `/codex` does today from Claude Code.
+
+**Why:** Codex users deserve the same cross-model challenge that Claude users get via `/codex`. Currently the flow is one-way (Claude→Codex). Codex users have no way to get a Claude second opinion.
+
+**Context:** The `/codex` skill template (`codex/SKILL.md.tmpl`) shows the pattern — it wraps `codex exec` with JSONL parsing, timeout handling, and structured output. The reverse skill would wrap `claude -p` with similar infrastructure. Would be generated into `.agents/skills/gstack-claude/` by `gen-skill-docs --host codex`.
+
+**Effort:** M (human: ~2 weeks / CC: ~30 min)
+**Priority:** P1
+**Depends on:** None
+
 ## Completeness
 
 ### Completeness metrics dashboard