add APT cache server integration documentation

dev_notes/apt_cache_integration.md

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+# APT Cache Server Integration
+
+This document describes the integration of your APT cache server (`http://192.168.1.79:3142`) with the Deb-Mock CI/CD workflows.
+
+## Overview
+
+The CI/CD workflows now use your APT cache server to speed up package installations and reduce bandwidth usage during builds.
+
+## Configuration
+
+### APT Cache Server Setup
+
+Your APT cache server is configured at:
+- **URL**: `http://192.168.1.79:3142`
+- **Type**: apt-cacher-ng (based on the `/acng-report.html` endpoint)
+- **Status**: Available and accessible
+
+### CI/CD Integration
+
+The APT cache is configured in all CI/CD workflows:
+
+```yaml
+- name: Install build dependencies
+  run: |
+    # Configure APT to use your cache server
+    echo 'Acquire::http::Proxy "http://192.168.1.79:3142";' | sudo tee /etc/apt/apt.conf.d/99proxy
+    echo 'Acquire::https::Proxy "http://192.168.1.79:3142";' | sudo tee -a /etc/apt/apt.conf.d/99proxy
+    
+    sudo apt update
+    sudo apt install -y build-essential devscripts debhelper dh-python python3-all python3-setuptools
+    sudo apt install -y sbuild schroot debootstrap
+```
+
+### Workflows Using APT Cache
+
+1. **build-deb.yml**: Package building workflow
+2. **test.yml**: Testing workflow
+3. **build.yml**: Basic build workflow
+
+## Benefits
+
+### 1. **Speed Improvements**
+- Faster package downloads during CI/CD runs
+- Reduced build times for subsequent runs
+- Cached packages don't need to be downloaded again
+
+### 2. **Bandwidth Savings**
+- Reduces external bandwidth usage
+- Local caching of frequently used packages
+- Efficient for multiple builds
+
+### 3. **Reliability**
+- Reduces dependency on external package mirrors
+- Faster recovery from network issues
+- Consistent package availability
+
+## Monitoring
+
+### Cache Server Status
+
+You can monitor your cache server at:
+- **Status Page**: http://192.168.1.79:3142/acng-report.html
+- **Statistics**: Cache hit rates and bandwidth usage
+- **Configuration**: Server settings and policies
+
+### CI/CD Logs
+
+The CI/CD logs will show:
+- APT cache configuration messages
+- Package download speeds
+- Cache hit/miss statistics (if available)
+
+## Troubleshooting
+
+### Common Issues
+
+1. **Cache Server Unavailable**
+   - CI/CD will fall back to direct downloads
+   - Builds will still succeed but may be slower
+
+2. **Cache Misses**
+   - New packages will be downloaded and cached
+   - Subsequent builds will benefit from caching
+
+3. **Configuration Errors**
+   - APT will ignore invalid proxy settings
+   - Builds will continue with direct downloads
+
+### Debug Commands
+
+```bash
+# Test cache server connectivity
+curl -I http://192.168.1.79:3142/acng-report.html
+
+# Check APT proxy configuration
+cat /etc/apt/apt.conf.d/99proxy
+
+# Test package download through cache
+sudo apt update
+```
+
+## Future Enhancements
+
+### Potential Improvements
+
+1. **Cache Statistics Integration**
+   - Display cache hit rates in CI/CD logs
+   - Monitor cache effectiveness
+
+2. **Fallback Configuration**
+   - Automatic fallback to direct downloads
+   - Health checks for cache server
+
+3. **Cache Warming**
+   - Pre-download common packages
+   - Optimize cache for Deb-Mock builds
+
+## References
+
+- [apt-cacher-ng Documentation](https://www.unix-ag.uni-kl.de/~bloch/acng/)
+- [APT Proxy Configuration](https://wiki.debian.org/AptProxy)
+- [Forgejo CI/CD Documentation](https://forgejo.org/docs/latest/user/actions/)