# Graph Overlay System (Policy, VEX, Reachability)

## Module
Graph

## Status
IMPLEMENTED

## Description
Overlay system with exporter, in-memory overlay service, and tests for layering policy/VEX/reachability data onto dependency graphs.

## Implementation Details
- **Overlay service interface**: `src/Graph/StellaOps.Graph.Api/Services/IOverlayService.cs` -- overlay query contract
- **In-memory overlay service**: `src/Graph/StellaOps.Graph.Api/Services/InMemoryOverlayService.cs` -- in-memory overlay implementation for testing
- **Overlay exporter**: `src/Graph/StellaOps.Graph.Indexer/Analytics/GraphOverlayExporter.cs` -- exports analytics results as overlay layers
- **Policy overlay processor**: `src/Graph/StellaOps.Graph.Indexer/Ingestion/Policy/PolicyOverlayProcessor.cs` -- ingests policy decisions as graph overlays
- **Policy overlay transformer**: `src/Graph/StellaOps.Graph.Indexer/Ingestion/Policy/PolicyOverlayTransformer.cs` -- transforms policy data for graph overlay
- **Policy overlay snapshot**: `src/Graph/StellaOps.Graph.Indexer/Ingestion/Policy/PolicyOverlaySnapshot.cs` -- policy overlay state
- **Policy overlay metrics**: `src/Graph/StellaOps.Graph.Indexer/Ingestion/Policy/PolicyOverlayMetrics.cs`, `IPolicyOverlayMetrics.cs` -- overlay processing metrics
- **VEX overlay**: `src/Graph/StellaOps.Graph.Indexer/Ingestion/Vex/VexOverlayTransformer.cs`, `VexOverlaySnapshot.cs` -- VEX verdict overlays on graph
- **Reachability delta**: `src/Graph/StellaOps.Graph.Api/Services/IReachabilityDeltaService.cs`, `InMemoryReachabilityDeltaService.cs` -- reachability annotation overlays
- **Tests**: `src/Graph/__Tests/StellaOps.Graph.Indexer.Tests/GraphOverlayExporterTests.cs`
- **Source**: Feature matrix scan

## E2E Test Plan
- [ ] Verify policy overlay renders policy decisions on graph nodes
- [ ] Test VEX overlay annotates graph with VEX verdict data
- [ ] Verify reachability overlay shows reachability status per edge
- [ ] Test overlay exporter generates valid overlay from analytics results
- [ ] Verify overlay stacking (multiple overlays on same graph)