🔌 Add Plugin System to Copilot SDK

CHANGELOG_PLUGINS.md

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+# Plugin System Changelog
+
+## Version 1.0.0 - 2026-01-17
+
+### 🎉 Initial Release - Complete Plugin System
+
+#### ✨ New Features
+
+**Plugin Infrastructure**
+- Added `Plugin` interface with 8 lifecycle hooks
+- Added `PluginContext` interface for hook parameters
+- Added `PluginManager` class for plugin lifecycle management
+- Added plugin data persistence per session
+- Added automatic plugin enable/disable tracking
+
+**Lifecycle Hooks**
+- `onLoad()` - Called when plugin loads
+- `onSessionCreated(context)` - Called on session creation
+- `onBeforeSend(context, options)` - Called before sending messages
+- `onSessionEvent(context, event)` - Called on every session event
+- `onCompactionStart(context, data)` - Called when compaction starts
+- `onCompactionComplete(context, data)` - Called after compaction
+- `onSessionEnd(context)` - Called when session ends
+- `onUnload()` - Called when plugin unloads
+
+**Slash Command System**
+- `/plugins` or `/plugins list` - List installed plugins
+- `/plugins available` - Browse available plugins
+- `/plugins install <name>` - Install plugin from registry
+- `/plugins enable <name>` - Enable disabled plugin
+- `/plugins disable <name>` - Disable plugin temporarily
+- `/plugins uninstall <name>` - Remove plugin completely
+- `/plugins help` - Show command help
+
+**Built-in Plugins** (4 included)
+- `memory-preservation` - Preserves conversation data before compaction
+- `logger` - Logs all session interactions
+- `analytics` - Tracks usage statistics
+- `anti-compaction` - Monitors and preserves during compaction
+
+**API Extensions**
+- Added `plugins` option to `CopilotClientOptions`
+- Added `pluginManagerConfig` option to `CopilotClientOptions`
+- Added `PluginManager` export
+- Added `BUILTIN_PLUGINS` registry export
+- Added plugin exports: `MemoryPreservationPlugin`, `LoggerPlugin`, `AnalyticsPlugin`, `AntiCompactionPlugin`
+
+#### 📁 New Files
+
+**Core Plugin System**
+- `nodejs/src/plugins.ts` - Plugin system core (600+ lines)
+- `nodejs/src/builtin-plugins.ts` - Built-in plugins (150+ lines)
+- `nodejs/src/anti-compaction-plugin.ts` - Anti-compaction plugin (100+ lines)
+
+**Testing & Examples**
+- `nodejs/test-plugin-system.js` - Comprehensive test suite (33 tests)
+- `nodejs/copilot-wrapper.js` - Interactive CLI wrapper example
+- `nodejs/test-plugin.js` - Simple test plugin example
+
+**Documentation**
+- `PLUGIN_SYSTEM.md` - Complete plugin system documentation
+- `CHANGELOG_PLUGINS.md` - This file
+
+#### 🔧 Modified Files
+
+**SDK Core Integration**
+- `nodejs/src/client.ts` - Added PluginManager initialization
+- `nodejs/src/session.ts` - Added plugin hook execution
+- `nodejs/src/types.ts` - Added plugin-related types
+- `nodejs/src/index.ts` - Added plugin exports
+
+#### ✅ Testing
+
+**Test Coverage** (100% pass rate)
+- ✅ PluginManager initialization (3 tests)
+- ✅ Slash command system (9 tests)
+- ✅ Plugin lifecycle hooks (5 tests)
+- ✅ Built-in plugins (5 tests)
+- ✅ Logger plugin functionality (2 tests)
+- ✅ Memory preservation plugin (1 test)
+- ✅ Analytics plugin (1 test)
+- ✅ Multiple plugins together (1 test)
+- ✅ Plugin data persistence (1 test)
+- ✅ Edge cases (5 tests)
+
+**Total**: 33/33 tests passing
+
+#### 🎯 Use Cases
+
+The plugin system enables:
+- **Session logging** - Debug and monitor interactions
+- **Analytics tracking** - Measure usage and performance
+- **Context preservation** - Save important data during compaction
+- **Message modification** - Transform prompts and responses
+- **Custom workflows** - Add domain-specific functionality
+- **Integration hooks** - Connect to external systems
+- **Security monitoring** - Track and audit usage
+- **Cost tracking** - Monitor token usage and costs
+
+#### 🚀 Performance
+
+- Zero overhead when no plugins loaded
+- Minimal overhead per plugin (microseconds per hook)
+- Async hook execution
+- No blocking operations in critical path
+- Memory efficient (plugin data per session)
+
+#### 🔒 Security
+
+- Plugins run in same process (trusted only)
+- Full SDK API access
+- No sandboxing (v1.0)
+- Plugin review recommended
+
+#### 📦 Distribution
+
+- Included in main SDK package
+- No additional dependencies
+- TypeScript definitions included
+- ESM module format
+
+#### 🎓 Examples
+
+See `copilot-wrapper.js` for complete working example:
+- Launches Copilot CLI in server mode
+- Connects via plugin-enabled SDK
+- Interactive readline interface
+- Full plugin support
+
+#### 🏴‍☠️ Credits
+
+**Development**: Barrer Software (@barrersoftware)
+**Base SDK**: GitHub Copilot SDK (MIT License)
+**License**: MIT
+
+---
+
+## Compatibility
+
+- ✅ Compatible with @github/copilot-sdk 1.0.0+
+- ✅ Node.js 18+
+- ✅ TypeScript 5.0+
+- ✅ ESM modules
+
+## Migration Guide
+
+No migration needed for existing SDK users. Plugin system is opt-in:
+
+```javascript
+// Before (still works)
+const client = new CopilotClient();
+
+// After (with plugins)
+const client = new CopilotClient({
+  plugins: [myPlugin]
+});
+```
+
+## Known Limitations
+
+1. No plugin sandboxing (v1.0)
+2. No plugin dependency management
+3. No plugin versioning
+4. Cannot prevent context compaction (SDK limitation)
+5. Plugins cannot add new SDK methods
+
+## Roadmap
+
+**Future Enhancements** (v2.0+)
+- [ ] Plugin sandboxing/isolation
+- [ ] Plugin dependency resolution
+- [ ] Plugin versioning system
+- [ ] Remote plugin registry
+- [ ] Plugin marketplace
+- [ ] Permission system
+- [ ] Plugin communication (IPC)
+- [ ] Hot reload support
+- [ ] Plugin debugging tools
+
+---
+
+**Questions?** See [PLUGIN_SYSTEM.md](PLUGIN_SYSTEM.md) for complete documentation.