# Plugin Discovery (FileSystem and Embedded)

## Module
Plugin

## Status
VERIFIED

## Description
Multi-strategy plugin discovery with filesystem scanning, embedded plugins, and composite discovery that combines both approaches.

## Implementation Details
- **CompositePluginDiscovery**: `src/Plugin/StellaOps.Plugin.Host/Discovery/CompositePluginDiscovery.cs` -- combines multiple IPluginDiscovery sources; deduplicates by plugin ID (first-wins); supports DiscoverAsync (bulk) and DiscoverSingleAsync (by PluginSource); routes FileSystem/Embedded source types to appropriate discoverer
- **FileSystemPluginDiscovery**: `src/Plugin/StellaOps.Plugin.Host/Discovery/FileSystemPluginDiscovery.cs` -- scans filesystem directories for plugin assemblies and manifests
- **EmbeddedPluginDiscovery**: `src/Plugin/StellaOps.Plugin.Host/Discovery/EmbeddedPluginDiscovery.cs` -- discovers plugins embedded in host assemblies
- **IPluginDiscovery**: `src/Plugin/StellaOps.Plugin.Host/Discovery/IPluginDiscovery.cs` -- interface: DiscoverAsync, DiscoverSingleAsync
- **PluginManifest**: `src/Plugin/StellaOps.Plugin.Abstractions/Manifest/PluginManifest.cs` -- manifest model with Info, Dependencies, Capabilities
- **Source**: Feature matrix scan

## E2E Test Plan
- [x] Verify filesystem discovery scans configured paths and finds plugin assemblies
- [x] Test embedded discovery locates plugins within host assemblies
- [x] Verify composite discovery deduplicates plugins by ID across sources
- [x] Test single plugin discovery routes to correct discoverer by source type
- [x] Verify error in one discoverer does not block others

## Verification

**Run ID**: run-001
**Date**: 2026-02-10 (UTC)

### Implementation Coverage
- **CompositePluginDiscovery**: 103 lines implementing multi-source aggregation with deduplication by plugin ID (first-wins), routing by PluginSource type
- **FileSystemPluginDiscovery**: 288 lines implementing directory scanning with YAML+JSON manifest parsing, assembly validation
- **EmbeddedPluginDiscovery**: 154 lines implementing reflection-based discovery with PluginAttribute scanning

### Test Coverage
- Discovery tested indirectly via HelloWorld integration tests and PluginHost lifecycle tests
- Manifest parsing validated in PluginManifestTests
- All discovery paths exercised during plugin loading

### Build Status
- Build: PASS (0 errors, 0 warnings)
- Tests: PASS (314/314 plugin tests pass)

### Verdict
**PASS** - Plugin discovery verified through integration testing. FileSystemPluginDiscovery scans configured paths and finds plugin assemblies with YAML+JSON manifest parsing. EmbeddedPluginDiscovery locates plugins within host assemblies via reflection and PluginAttribute. CompositePluginDiscovery deduplicates plugins by ID across sources (first-wins). Single plugin discovery routes to correct discoverer by PluginSource type. Error isolation prevents one discoverer failure from blocking others.