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Installing Canon Boundary Guard adds the plugin to your Codex environment, makes the $canon-boundary-guard skill available for session activation, and — if you choose — wires the bundled PreToolUse hook so the compact classification frame is automatically re-injected before matched write operations. Installation is handled entirely through the Codex plugin system; no manual file copying is required for the standard setup.

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Install the Plugin

1

Add the repository via the marketplace

Run the following command to register the Canon Boundary Guard repository as a Codex plugin source:
codex plugin marketplace add XxYouDeaDPunKxX/canon-boundary-guard-codex
This makes the plugin available in Codex but does not yet enable it.
2

Enable Canon Boundary Guard in the plugin picker

Open Codex and navigate to the plugin list. In Codex UIs that support slash commands, open the plugin picker with:
/plugins
Find Canon Boundary Guard in the list and enable it. The skill and hook bundle will be registered with your Codex installation.
3

Activate in a new thread

Start a new Codex thread and tell Codex to use the plugin for the session:
Use Canon Boundary Guard for this session.
Codex will read the full SKILL.md frame and adopt the provenance classification posture silently — no confirmation message is shown. The frame remains active for the duration of the session.

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Enabling the Hook

The PreToolUse hook is optional but recommended for sessions where repository content, project rules, naming conventions, workflows, or AGENTS.md authority may be relevant. Without the hook, the classification frame is still fully active via the skill — the hook only re-surfaces the compact frame at the exact moment a write tool is called, as an additional reinforcement layer.
To enable the bundled hook, add the following to your Codex config.toml: 
[features]
hooks = true
plugin_hooks = true
After saving the configuration, restart Codex so the hook registration takes effect. Once Codex is running again, review and trust the bundled hook:
  • If your Codex UI exposes /hooks — open the hook review view and trust the Canon Boundary Guard hook listed there.
  • In editor integrations where /hooks is not available — open the plugin details panel or approve the hook when Codex shows the trust prompt.
Plugin-bundled hooks are non-managed hooks and will not run until explicitly trusted. The bundled hook configuration targets apply_patch, Write, and Edit operations: 
{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "apply_patch|Write|Edit",
        "hooks": [
          {
            "type": "command",
            "command": "python ${PLUGIN_ROOT}/skills/canon-boundary-guard/scripts/inject_frame.py",
            "timeout": 5,
            "statusMessage": "Provenance frame"
          }
        ]
      }
    ]
  }
}
The hook emits the classification frame as hookSpecificOutput.additionalContext (the model-visible context path for PreToolUse) and also surfaces it as a systemMessage so the hook activity remains visible in the UI or event stream. It does not block the tool call or modify the requested operation.
The hook command uses python by default. If your system requires python3, you must adjust the hook command in your local plugin copy or configure an equivalent hook entry in your Codex config.toml that uses python3 explicitly. Failing to do this on a python3-only system will cause the hook to silently fail to execute.

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Legacy and Manual Setup

If you prefer to manage the skill manually without the plugin system — for example, to pin a specific version or to inspect and modify the skill files directly before use — the older standalone layout is preserved in the standalone-skill-v1 branch of the repository. Check out that branch and copy the canon-boundary-guard/ folder into your Codex skills directory. Note that the standalone branch does not include the plugin manifest or the hook bundle; hook setup must be done manually if desired.

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