feat(dev): add containerized development environment

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

dev/README.md

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+# ZeroClaw Development Environment
+
+A fully containerized development sandbox for ZeroClaw agents. This environment allows you to develop, test, and debug the agent in isolation without modifying your host system.
+
+## Directory Structure
+
+- **`agent/`**: (Merged into root Dockerfile)
+  - The development image is built from the root `Dockerfile` using the `dev` stage (`target: dev`).
+  - Based on `debian:bookworm-slim` (unlike production `distroless`).
+  - Includes `bash`, `curl`, and debug tools.
+- **`sandbox/`**: Dockerfile for the simulated user environment.
+  - Based on `ubuntu:22.04`.
+  - Pre-loaded with `git`, `python3`, `nodejs`, `npm`, `gcc`, `make`.
+  - Simulates a real developer machine.
+- **`docker-compose.yml`**: Defines the services and `dev-net` network.
+- **`cli.sh`**: Helper script to manage the lifecycle.
+
+## Usage
+
+Run all commands from the repository root using the helper script:
+
+### 1. Start Environment
+```bash
+./dev/cli.sh up
+```
+Builds the agent from source and starts both containers.
+
+### 2. Enter Agent Container (`zeroclaw-dev`)
+```bash
+./dev/cli.sh agent
+```
+Use this to run `zeroclaw` CLI commands manually, debug the binary, or check logs internally.
+- **Path**: `/zeroclaw-data`
+- **User**: `nobody` (65534)
+
+### 3. Enter Sandbox (`sandbox`)
+```bash
+./dev/cli.sh shell
+```
+Use this to act as the "user" or "environment" the agent interacts with.
+- **Path**: `/home/developer/workspace`
+- **User**: `developer` (sudo-enabled)
+
+### 4. Development Cycle
+1. Make changes to Rust code in `src/`.
+2. Rebuild the agent:
+   ```bash
+   ./dev/cli.sh build
+   ```
+3. Test changes inside the container:
+   ```bash
+   ./dev/cli.sh agent
+   # inside container:
+   zeroclaw --version
+   ```
+
+### 5. Persistence & Shared Workspace
+The local `playground/` directory (in repo root) is mounted as the shared workspace:
+- **Agent**: `/zeroclaw-data/workspace`
+- **Sandbox**: `/home/developer/workspace`
+
+Files created by the agent are visible to the sandbox user, and vice versa.
+
+The agent configuration lives in `target/.zeroclaw` (mounted to `/zeroclaw-data/.zeroclaw`), so settings persist across container rebuilds.
+
+### 6. Cleanup
+Stop containers and remove volumes and generated config:
+```bash
+./dev/cli.sh clean
+```
+**Note:** This removes `target/.zeroclaw` (config/DB) but leaves the `playground/` directory intact. To fully wipe everything, manually delete `playground/`.