# Graph Node/Edge Model with Overlays

## Module
Attestor

## Status
VERIFIED

## Description
Graph module has core node/edge model with overlay services, query APIs, and analytics. ProofChain library in Attestor also maintains its own graph node/edge/subgraph types.

## Implementation Details
- **Proof Graph Nodes**: `src/Attestor/__Libraries/StellaOps.Attestor.ProofChain/Graph/ProofGraphNode.cs` -- typed graph node (Evidence, Verdict, Policy, Artifact) with content-addressed ID and metadata.
- **Proof Graph Edges**: `Graph/ProofGraphEdge.cs` -- directed edge between nodes with `ProofGraphEdgeType.cs` (DependsOn, Produces, Validates, etc.).
- **Node Types**: `Graph/ProofGraphNodeType.cs` -- enum: Evidence, Verdict, Policy, Artifact.
- **Edge Types**: `Graph/ProofGraphEdgeType.cs` -- enum defining relationship semantics between graph nodes.
- **In-Memory Graph Service**: `Graph/InMemoryProofGraphService.cs` (with `.Mutation`, `.Queries`, `.Subgraph`) -- full graph service supporting node/edge CRUD, traversal queries, and subgraph extraction.
- **Subgraph Extraction**: `Graph/ProofGraphSubgraph.cs` -- extracts a subgraph rooted at a specific node (e.g., all evidence for a verdict).
- **Graph Paths**: `Graph/ProofGraphPath.cs` -- represents a traversal path through the graph with ordered node sequence.
- **Graph Root Attestor**: `__Libraries/StellaOps.Attestor.GraphRoot/GraphRootAttestor.cs` -- attests Merkle roots over graph structures. `IGraphRootAttestor.cs` -- interface.
- **Graph Types**: `__Libraries/StellaOps.Attestor.GraphRoot/GraphType.cs` -- supported graph types (ResolvedExecutionGraph, ReachabilityGraph, DependencyGraph, ProofSpine, EvidenceGraph).
- **Tests**: `__Tests/StellaOps.Attestor.ProofChain.Tests/` -- graph service tests.

## E2E Test Plan
- [ ] Create nodes of each `ProofGraphNodeType` (Evidence, Verdict, Policy, Artifact) via `InMemoryProofGraphService` and verify they are retrievable by ID
- [ ] Add edges of different `ProofGraphEdgeType` between nodes and verify edge traversal returns correct neighbors
- [ ] Build a Verdict -> Reasoning -> Evidence chain and extract a `ProofGraphSubgraph` rooted at the verdict; verify all descendants are included
- [ ] Query `ProofGraphPath` from a verdict to a leaf evidence node and verify path length and node type ordering
- [ ] Add overlay edges (e.g., cross-linking two evidence nodes) and verify the mutation is reflected in subsequent queries
- [ ] Delete a node via `.Mutation` and verify cascading edge removal
- [ ] Verify content-addressed node IDs: adding two nodes with identical content produces the same ID

## Verification

| Check | Result |
|-------|--------|
| Tier 0 - Source Verification | PASS |
| Tier 1 - Build + Code Review | PASS |
| Tier 2 - Behavioral Verification | PASS |
| Verified Date | 2026-02-13 |
| Run ID | run-001 |