Upgrade Codex capability boundary

[yangshu2087]

Summary

Upgrades the local Codex capability boundary after checking current OpenAI Codex docs, npm/GitHub releases, and high-signal skill catalogs.

Key changes:

• Adds project-scoped custom agents under .codex/agents/:
  • pr_explorer
  • reviewer
  • docs_researcher
  • browser_debugger
  • ui_fixer
• Adds docs/codex-capability-boundary-upgrade-2026-04-23.md with source-backed decisions and routing rules.
• Adds scripts/codex-boundary-smoke.sh to validate version/config/features/MCP/custom-agent boundary.

Local user-level changes made outside this repo:

• Upgraded standalone CLI from codex-cli 0.122.0-alpha.5 to stable codex-cli 0.124.0.
• Backed up old binary under /Users/yangshu/.local/bin/codex-backups/.
• Updated /Users/yangshu/.codex/config.toml:
  • default gpt-5.5/high
  • review model gpt-5.5
  • frontier profile for gpt-5.5/xhigh
  • guarded profile with approvals_reviewer = "auto_review"
  • explicit features.memories = false while Memories remain experimental locally.

Sources reviewed

• OpenAI Codex Best Practices
• OpenAI Codex Customization
• OpenAI Codex Config Reference
• OpenAI Codex Skills
• OpenAI Codex Plugins
• OpenAI Codex Models
• OpenAI Codex Subagents
• OpenAI Codex GitHub Integration
• OpenAI Codex Security / Agent approvals & security
• openai/codex release rust-v0.124.0
• openai/skills
• ComposioHQ/awesome-codex-skills
• shinpr/awesome-codex-workflows
• Public X/OpenAIDevs signal, used only as discovery context.

Verification

• codex --version → codex-cli 0.124.0
• /Users/yangshu/Codex/scripts/check-codex-upgrade.sh
• /Users/yangshu/Codex/scripts/codex-boundary-smoke.sh
• CODEX_CREATIVE_UI_SMOKE_OUT=/tmp/codex-creative-ui-smoke-20260423 /Users/yangshu/Codex/scripts/codex-creative-ui-smoke.sh /Users/yangshu/Codex
• CODEX_REGRESSION_PROFILE_TIMEOUT_SECONDS=240 CODEX_REGRESSION_BROWSER_URL=https://example.com /Users/yangshu/Codex/scripts/codex-quality-regression.sh
• git diff --check -- .codex/agents docs/codex-capability-boundary-upgrade-2026-04-23.md scripts/codex-boundary-smoke.sh
• bash -n scripts/codex-boundary-smoke.sh

Browser evidence:

• /tmp/codex-quality-regression-20260423-215257/agent-browser-smoke-20260423-215315.png
• /tmp/codex-creative-ui-smoke-20260423/agent-browser-smoke-20260423-215240.png

Known gaps

• Existing local dirty files unrelated to this PR remain uncommitted on the workstation.
• Official Memories remain experimental locally and are explicitly disabled in config; the repo continues using the audited Markdown/JSONL memory layer.
• Current runtime pressure reported high swap, so large parallel fanout should stay bounded.