global-agent-guardrails git:20260926.7dce66cA

Immutable. This exact content never changes and is served at /api/v1/blob/bd641569158b319e.

---
name: global-agent-guardrails
description: "Configure the shared guard against catastrophic shell commands in local AI agents. Use when changing block patterns, adding an agent or machine, or investigating why a command was or wasn't blocked."
---

# Global Agent Guardrails

Block catastrophic shell commands before execution. One patterns file feeds a shared hook script or native adapter for each agent. This guards against accidents, not malicious agents (obfuscation like `python -c "shutil.rmtree(...)"` can slip past regex).

## File map

```
<GUARD_DIR>/dangerous-patterns.txt   # THE denylist: one POSIX-ERE regex per line, # comments
<GUARD_DIR>/deny-dangerous.sh        # shared guard: hook JSON on stdin -> exit 2 blocks
<GUARD_DIR>/test-guard.sh            # test suite: run after ANY pattern change
~/.config/opencode/plugins/command-guard.ts   # OpenCode adapter (throws to block)
~/.pi/agent/extensions/command-guard.ts       # Pi adapter (returns {block:true})
~/.hermes/plugins/command-guard/              # Hermes plugin (returns {"action":"block"})
```

## Check installation

```bash
ls <GUARD_DIR>/deny-dangerous.sh <GUARD_DIR>/dangerous-patterns.txt
<GUARD_DIR>/test-guard.sh   # must end "failed: 0"
```

If missing, rebuild from the wiring table (history: project research notes).

## Add or tune a pattern

1. Edit `<GUARD_DIR>/dangerous-patterns.txt`. Write POSIX ERE (`grep -E`). Use `[[:space:]]`, never `\\s` — adapters auto-convert `[:space:]` to `\\s` for JS/Python and compile in multiline mode.
2. Add block and allow cases to `test-guard.sh`, then run it; all must pass.
3. Verify the new pattern compiles in the adapter engines:

```bash
python3 -c 'import re,pathlib; [re.compile(l.strip().replace("[:space:]",r"\s"),re.M) for l in pathlib.Path("<GUARD_DIR>/dangerous-patterns.txt").read_text().splitlines() if l.strip() and not l.startswith("#")]; print("ok")'
```

4. Consumers re-read patterns for every command. Exception: Droid uses `commandBlocklist` in `~/.factory/settings.json` — mirror changes there manually.

Block only catastrophic commands (irreversible data loss, disk wipes, repo deletion). Recoverable local commands (`git status`, `git clean -fdx`, `rm -rf node_modules`) stay allowed; avoid over-blocking. Keep routine login and credential-management commands outside catastrophic-command rules.

Password-manager and secret-store access should be governed by a separate, locally chosen policy; do not publish private denylist entries or storage locations here.

## Per-agent wiring (user-global)

| Agent | Config | Event | Blocks via |
|---|---|---|---|
| Claude Code | `~/.claude/settings.json` | `PreToolUse` matcher `Bash` | shared script, exit 2 |
| Codex CLI/app/IDE | `~/.codex/hooks.json` | `PreToolUse` matcher `Bash` | shared script, exit 2 |
| Cursor IDE + CLI | `~/.cursor/hooks.json` | `beforeShellExecution` | shared script with `cursor` arg, deny JSON |
| Grok (xAI) | auto-loads Claude + Cursor hook files (compat on by default); native option `~/.grok/hooks/*.json` | `PreToolUse` | shared script (reads `.toolInput.command`) |
| OpenCode | `~/.config/opencode/plugins/command-guard.ts` | `tool.execute.before` | adapter throws Error |
| Pi | `~/.pi/agent/extensions/command-guard.ts` | `pi.on("tool_call")` | adapter returns `{block:true}` |
| Hermes | `~/.hermes/plugins/command-guard/` (`plugin.yaml` + `__init__.py`) | `pre_tool_call` hook | plugin returns `{"action":"block"}` |
| Droid (Factory) | `~/.factory/settings.json` | native `commandBlocklist` | hard-block, no approval possible |
| Devin CLI | `~/.config/devin/config.json` | `PreToolUse` matcher `^exec$` | shared script, exit 2 |

Claude/Codex hook entry; for Devin, replace `Bash` with `^exec$`. Merge into the existing `hooks` object; never overwrite it:

```json
{"hooks": {"PreToolUse": [{"matcher": "Bash", "hooks": [{"type": "command", "command": "/ABSOLUTE/PATH/TO/deny-dangerous.sh"}]}]}}
```

Cursor entry (payload has `.command`, so pass the `cursor` arg):

```json
{"beforeShellExecution": [{"command": "/ABSOLUTE/PATH/TO/deny-dangerous.sh cursor", "failClosed": false}]}
```

Use absolute paths in configs (`~` expansion is inconsistent across agents).

## Gotchas

- **Codex trust is hash-pinned.** Any edit to the hook ENTRY in `hooks.json` (not the patterns file) invalidates trust; run `/hooks` in Codex and re-trust, else Codex silently skips the guard. Trust hashes live in `[hooks.state]` in `~/.codex/config.toml` and are shared by CLI, desktop app, and IDE extension. For CI or scripts, follow the tool's documented trust configuration.
- **Cursor `failClosed` behavior depends on the runtime.** Check the agent's documentation and choose a setting appropriate to its support for hook scripts.
- **Hermes plugin manifest key is `provides_hooks`** (not `hooks`). Plugin must be enabled in its configuration. The CLI enable command may prompt interactively and hang non-interactive shells. Hermes hooks are fail-open on exceptions — keep the plugin trivial. Shell tool name is `terminal`.
- **Pi `tool_call` handler errors block the tool** (fail-safe) — adapter must catch its own errors and fail open, or a broken patterns file bricks every bash call.
- **Droid semantics:** `commandDenylist` = ask for confirmation; `commandBlocklist` = never runs, even at full autonomy. Use blocklist for catastrophic entries.
- **Guard script payload detection:** command lives at `.tool_input.command` (Claude/Codex/Devin), `.toolInput.command` (Grok), `.command` (Cursor). Keep all three in the jq fallback chain.
- **Adapter regexes require multiline mode.** Keep JavaScript's `m` flag and Python's `re.M` so `^` matches each shell line like `grep`.
- **False-positive class:** a harmless command whose ARGUMENT text contains a dangerous-looking string (e.g. passing a prompt mentioning `git push --force` on a CLI) gets blocked. Workaround: put the text in a file and reference it.
- Some agents or remote/background modes may not support local hooks. Verify hook coverage for each runtime you use.

## E2E verification

Safe probe: ask the agent to run `git push --force` from a NON-git directory — blocked = guard works; "not a git repository" = guard failed but no harm done. Run probes using the agent's documented command interface and permission settings.

Direct script test:

```bash
echo '{"tool_input":{"command":"rm -rf /"}}' | <GUARD_DIR>/deny-dangerous.sh; echo "exit=$?"   # expect exit=2
```