Codex adapter split + hook enforcement port + output gating

[5uck1ess]

Summary

• Split Codex adapter into separate devkit-codex repo; this branch keeps shared engine behavior here (98bddc3, 6fb14b4)
• Port Claude's hook enforcement model to Codex via the new adapter (e0a7302, de6f981)
• Add workflow required_outputs validation so steps can declare and the engine can gate on produced artifacts (c807c6f, abc7078)

Tested in-session

• devkit-codex smoke suite: 22 passed, 0 failed (test/hooks_test.sh), including the new install sets devkit MCP CLAUDE_PLUGIN_ROOT assertion
• MCP handshake probe from a temp consumer repo with no workflows/:
  • Without CLAUDE_PLUGIN_ROOT: devkit_list correctly errors with no workflows directory: …
  • With CLAUDE_PLUGIN_ROOT (as emitted by the paired devkit-codex install.sh fix, commit 6356c9a): devkit_list returns all 22 workflows
• Engine rebuilds cleanly: v2.1.29-6-gabc7078

Pairs with

• devkit-codex commit 6356c9a ("Set devkit MCP plugin root") — emits env = { CLAUDE_PLUGIN_ROOT = … } in the [mcp_servers.devkit] block so the engine resolves workflows/ against the devkit install, not the consumer cwd.

Test plan (real Codex session, post-window-reset)

• bash devkit-codex/install.sh --devkit /path/to/devkit against real ~/.codex/config.toml
• codex mcp list shows devkit healthy in a fresh shell
• Disposable consumer repo (no workflows/) — devkit_list returns 22 workflows
• /feature … slash command starts the feature workflow via slash bridge
• Natural-language trigger: "please run a security audit" starts tri-security
• PreToolUse permission-guard denies rm -rf mid-workflow
• install.sh --uninstall removes only devkit-owned config/hooks, preserves any [mcp_servers.other] block