semi implemented and features implemented save checkpoint

docs/features/unchecked/reachgraph/reachability-analysis-with-call-graph-evidence.md

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+# Reachability Analysis with Call Graph Evidence
+
+## Module
+ReachGraph
+
+## Status
+IMPLEMENTED
+
+## Description
+Reachability analysis is implemented with a dedicated ReachGraph backend service, frontend reachability explanation views, and witness path components showing call graph evidence traces.
+
+## Implementation Details
+- **ReachGraphController**: `src/ReachGraph/StellaOps.ReachGraph.WebService/Controllers/ReachGraphController.cs` -- REST API at `v1/reachgraphs` with slice queries supporting call graph evidence; GET `{digest}/slice` with `q` (package), `cve`, `entrypoint`, `file` query parameters
+- **IReachGraphSliceService**: `src/ReachGraph/StellaOps.ReachGraph.WebService/Services/IReachGraphSliceService.cs` -- `SliceByPackageAsync`, `SliceByCveAsync` (returns `CveSliceResponse` with `Sinks` and `Paths`), `SliceByEntrypointAsync`, `SliceByFileAsync`
+- **ReachGraphSliceService**: `src/ReachGraph/StellaOps.ReachGraph.WebService/Services/ReachGraphSliceService.cs` -- cached slice computation with `IReachGraphCache`
+- **ReachabilityPath model**: `src/ReachGraph/StellaOps.ReachGraph.WebService/Models/ReachGraphContracts.cs` -- `Entrypoint`, `Sink`, `Hops` (call chain), `Edges` (graph edges showing evidence trace)
+- **CveSliceResponse**: `src/ReachGraph/StellaOps.ReachGraph.WebService/Models/ReachGraphContracts.cs` -- extends `SliceQueryResponse` with `Sinks` and `Paths` for call graph evidence
+- **IReachabilityIndex**: `src/__Libraries/StellaOps.Reachability.Core/IReachabilityIndex.cs` -- unified facade with `QueryStaticAsync`, `QueryRuntimeAsync`, `QueryHybridAsync` combining static call graph with runtime evidence
+- **EvidenceUriBuilder**: `src/__Libraries/StellaOps.Reachability.Core/EvidenceUriBuilder.cs` -- builds URIs for evidence artifacts
+- **Frontend**: reachability explanation views and witness path components in `src/Web/`
+- **Tests**: `src/ReachGraph/__Tests/StellaOps.ReachGraph.WebService.Tests/ReachGraphApiIntegrationTests.cs`
+- **Source**: Feature matrix scan
+
+## E2E Test Plan
+- [ ] Verify CVE slice returns reachability paths with entrypoint-to-sink hops
+- [ ] Test call graph evidence trace includes edge types and evidence URIs
+- [ ] Verify package slice shows upstream/downstream reachability with configurable depth
+- [ ] Test entrypoint slice traces all paths from a given entrypoint
+- [ ] Verify file-based slice returns reachability for symbols in a specific file
+- [ ] Test frontend reachability explanation view renders witness paths correctly