dcg

What this skill does

# DCG — Destructive Command Guard

A high-performance Claude Code hook that intercepts and blocks destructive commands before they execute. Written in Rust with SIMD-accelerated filtering for sub-millisecond latency.

## Why This Exists

AI coding agents are powerful but fallible. They can accidentally run destructive commands:

- **"Let me clean up the build artifacts"** → `rm -rf ./src` (typo)
- **"I'll reset to the last commit"** → `git reset --hard` (destroys uncommitted changes)
- **"Let me fix the merge conflict"** → `git checkout -- .` (discards all modifications)
- **"I'll clean up untracked files"** → `git clean -fd` (permanently deletes untracked files)

DCG intercepts dangerous commands *before* execution and blocks them with a clear explanation, giving you a chance to stash your changes first.

## Critical Design Principles

### 1. Whitelist-First Architecture

Safe patterns are checked *before* destructive patterns. This ensures explicitly safe commands are never accidentally blocked:

```
git checkout -b feature    →  Matches SAFE "checkout-new-branch"  →  ALLOW
git checkout -- file.txt   →  No safe match, matches DESTRUCTIVE  →  DENY
```

### 2. Fail-Safe Defaults (Default-Allow)

Unrecognized commands are **allowed by default**. This ensures:
- The hook never breaks legitimate workflows
- Only *known* dangerous patterns are blocked
- New git commands work until explicitly categorized

### 3. Zero False Negatives Philosophy

The pattern set prioritizes **never allowing dangerous commands** over avoiding false positives. A few extra prompts for manual confirmation are acceptable; lost work is not.

## What It Blocks

### Git Commands That Destroy Uncommitted Work

| Command | Reason |
|---------|--------|
| `git reset --hard` | Destroys uncommitted changes |
| `git reset --merge` | Destroys uncommitted changes |
| `git checkout -- <file>` | Discards file modifications |
| `git restore <file>` (without `--staged`) | Discards uncommitted changes |
| `git clean -f` | Permanently deletes untracked files |

### Git Commands That Destroy Remote History

| Command | Reason |
|---------|--------|
| `git push --force` / `-f` | Overwrites remote commits |
| `git branch -D` | Force-deletes without merge check |

### Git Commands That Destroy Stashed Work

| Command | Reason |
|---------|--------|
| `git stash drop` | Permanently deletes a stash |
| `git stash clear` | Permanently deletes all stashes |

### Filesystem Commands

| Command | Reason |
|---------|--------|
| `rm -rf` (outside `/tmp`, `/var/tmp`, `$TMPDIR`) | Recursive deletion is dangerous |

## What It ALLOWS

Safe operations pass through silently:

### Always Safe Git Operations

`git status`, `git log`, `git diff`, `git add`, `git commit`, `git push`, `git pull`, `git fetch`, `git branch -d` (safe delete with merge check), `git stash`, `git stash pop`, `git stash list`

### Explicitly Safe Patterns

| Pattern | Why Safe |
|---------|----------|
| `git checkout -b <branch>` | Creating new branches |
| `git checkout --orphan <branch>` | Creating orphan branches |
| `git restore --staged <file>` | Unstaging only, doesn't touch working tree |
| `git restore -S <file>` | Short flag for staged |
| `git clean -n` / `--dry-run` | Preview mode, no actual deletion |
| `rm -rf /tmp/*` | Temp directories are ephemeral |
| `rm -rf $TMPDIR/*` | Shell variable forms |

### Safe Alternative: `--force-with-lease`

```bash
git push --force-with-lease   # ALLOWED - refuses if remote has unseen commits
git push --force              # BLOCKED - can overwrite others' work
```

## Modular Pack System

DCG uses a modular "pack" system to organize patterns by category:

### Core Packs (Always Enabled)

| Pack | Description |
|------|-------------|
| `core.git` | Destructive git commands |
| `core.filesystem` | Dangerous rm -rf outside temp |

### Database Packs

| Pack | Description |
|------|-------------|
| `database.postgresql` | DROP/TRUNCATE in PostgreSQL |
| `database.mysql` | DROP/TRUNCATE in MySQL/MariaDB |
| `database.mongodb` | dropDatabase, drop() |
| `database.redis` | FLUSHALL/FLUSHDB |
| `database.sqlite` | DROP in SQLite |

### Container Packs

| Pack | Description |
|------|-------------|
| `containers.docker` | docker system prune, docker rm -f |
| `containers.compose` | docker-compose down --volumes |
| `containers.podman` | podman system prune |

### Kubernetes Packs

| Pack | Description |
|------|-------------|
| `kubernetes.kubectl` | kubectl delete namespace |
| `kubernetes.helm` | helm uninstall |
| `kubernetes.kustomize` | kustomize delete patterns |

### Cloud Provider Packs

| Pack | Description |
|------|-------------|
| `cloud.aws` | Destructive AWS CLI commands |
| `cloud.gcp` | Destructive gcloud commands |
| `cloud.azure` | Destructive az commands |

### Infrastructure Packs

| Pack | Description |
|------|-------------|
| `infrastructure.terraform` | terraform destroy |
| `infrastructure.ansible` | Dangerous ansible patterns |
| `infrastructure.pulumi` | pulumi destroy |

### System Packs

| Pack | Description |
|------|-------------|
| `system.disk` | dd, mkfs, fdisk operations |
| `system.permissions` | Dangerous chmod/chown patterns |
| `system.services` | systemctl stop/disable patterns |

### Other Packs

| Pack | Description |
|------|-------------|
| `strict_git` | Extra paranoid git protections |
| `package_managers` | npm unpublish, cargo yank |

### Configuring Packs

```toml
# ~/.config/dcg/config.toml
[packs]
enabled = [
    "database.postgresql",
    "containers.docker",
    "kubernetes",  # Enables all kubernetes sub-packs
]
```

## Environment Variables

| Variable | Description |
|----------|-------------|
| `DCG_PACKS="containers.docker,kubernetes"` | Enable packs (comma-separated) |
| `DCG_DISABLE="kubernetes.helm"` | Disable packs/sub-packs |
| `DCG_VERBOSE=1` | Verbose output |
| `DCG_COLOR=auto\|always\|never` | Color mode |
| `DCG_BYPASS=1` | Bypass DCG entirely (escape hatch) |

## Installation

### Quick Install (Recommended)

```bash
curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/destructive_command_guard/master/install.sh?$(date +%s)" | bash

# Easy mode: auto-update PATH
curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/destructive_command_guard/master/install.sh?$(date +%s)" | bash -s -- --easy-mode

# System-wide (requires sudo)
curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/destructive_command_guard/master/install.sh?$(date +%s)" | sudo bash -s -- --system
```

### From Source (Requires Rust Nightly)

```bash
cargo +nightly install --git https://github.com/Dicklesworthstone/destructive_command_guard
```

### Prebuilt Binaries

Available for: Linux x86_64, Linux ARM64, macOS Intel, macOS Apple Silicon, Windows

## Claude Code Configuration

Add to `~/.claude/settings.json`:

```json
{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Bash",
        "hooks": [
          {
            "type": "command",
            "command": "dcg"
          }
        ]
      }
    ]
  }
}
```

**Important:** Restart Claude Code after adding the hook.

## How It Works

### Processing Pipeline

```
┌─────────────────────────────────────────────────────────────────┐
│                        Claude Code                               │
│  Agent executes `rm -rf ./build`                                │
└─────────────────────┬───────────────────────────────────────────┘
                      │
                      ▼ PreToolUse hook (stdin: JSON)
┌─────────────────────────────────────────────────────────────────┐
│                          dcg                                     │
│  ┌──────────────┐    ┌──────────────┐    ┌──────────────┐       │
│  │    Parse     │───▶│  Normalize   │───▶│ Quick Reject │       │
│  │    JSON      │    │   Command    │    │   Filter     │       │
│  └──────────────┘    └──────────────┘    └──────┬───────┘       │
│                                                  │