Add CLAUDE.md with project guidance for Claude Code

- Project overview and architecture description
- Common development commands for building and testing
- Environment variables and configuration details
- Version management and automated update process
- Volume structure and data organization

🤖 Generated with [Claude Code](https://claude.ai/code)

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

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+This is a Docker image for running a Factorio headless server. It provides automated builds for multiple Factorio versions (stable and experimental) and supports both AMD64 and ARM64 architectures.
+
+## Architecture
+
+### Key Components
+
+1. **Docker Image Build System**
+   - `build.py` - Python script that builds Docker images from `buildinfo.json`
+   - `docker/Dockerfile` - Main Dockerfile that creates the Factorio server image
+   - `buildinfo.json` - Contains version info, SHA256 checksums, and tags for all supported versions
+   - Supports multi-architecture builds (linux/amd64, linux/arm64) using Docker buildx
+
+2. **Automated Updates**
+   - `update.sh` - Checks for new Factorio releases and updates `buildinfo.json`
+   - Updates README.md with new version tags
+   - Commits changes and tags releases automatically
+   - Run by GitHub Actions to keep images up-to-date
+
+3. **Container Scripts**
+   - `docker/files/docker-entrypoint.sh` - Main entrypoint that configures and starts the server
+   - `docker/files/docker-update-mods.sh` - Updates mods on server start
+   - `docker/files/docker-dlc.sh` - Manages DLC (Space Age) activation
+   - `docker/files/scenario.sh` - Alternative entrypoint for launching scenarios
+   - `docker/files/players-online.sh` - Checks if players are online (for watchtower integration)
+
+4. **RCON Client**
+   - `docker/rcon/` - C source for RCON client, built during Docker image creation
+   - Allows sending commands to the running server
+
+## Common Development Commands
+
+### Building Images
+
+```bash
+# Build a single architecture image locally
+python3 build.py
+
+# Build and push multi-architecture images
+python3 build.py --multiarch --push-tags
+```
+
+### Running the Container
+
+```bash
+# Basic run command
+docker run -d \
+  -p 34197:34197/udp \
+  -p 27015:27015/tcp \
+  -v /opt/factorio:/factorio \
+  --name factorio \
+  factoriotools/factorio
+
+# Using docker-compose
+docker-compose up -d
+```
+
+### Linting
+
+```bash
+# Lint Dockerfiles
+./lint.sh
+```
+
+### Testing Updates
+
+```bash
+# Check for new Factorio versions and update buildinfo.json
+./update.sh
+```
+
+## Key Configuration
+
+### Environment Variables
+- `LOAD_LATEST_SAVE` - Load the most recent save (default: true)
+- `GENERATE_NEW_SAVE` - Generate a new save if none exists (default: false)
+- `SAVE_NAME` - Name of the save file to load/create
+- `UPDATE_MODS_ON_START` - Update mods before starting (requires USERNAME/TOKEN)
+- `DLC_SPACE_AGE` - Enable/disable Space Age DLC (default: true)
+- `PORT` - UDP port for game server (default: 34197)
+- `RCON_PORT` - TCP port for RCON (default: 27015)
+
+### Volume Structure
+All data is stored in a single volume mounted at `/factorio`:
+```
+/factorio/
+├── config/           # Server configuration files
+├── mods/            # Game modifications
+├── saves/           # Save games
+├── scenarios/       # Scenario files
+└── script-output/   # Script output directory
+```
+
+## Version Management
+
+The project maintains compatibility with multiple Factorio versions:
+- Latest experimental version gets the `latest` tag
+- Latest stable version gets the `stable` tag
+- Each version also gets specific tags (e.g., `2.0.55`, `2.0`, `2`)
+- Legacy versions back to 0.12 are supported
+
+Version updates are automated via GitHub Actions that run `update.sh` periodically.
+
+## Testing Changes
+
+1. Modify `buildinfo.json` to test specific versions
+2. Run `python3 build.py` to build locally
+3. Test the container with your local data volume
+4. For production changes, ensure `update.sh` handles version transitions correctly