semi implemented and features implemented save checkpoint

docs/features/unchecked/attestor/reachability-graph-service.md

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+# Reachability Graph Service (Slice and Replay)
+
+## Module
+Attestor
+
+## Status
+IMPLEMENTED
+
+## Description
+Full reachability graph service with slice extraction, deterministic replay, storage, and REST API.
+
+## Implementation Details
+- **Reachability Subgraph Predicate**: `src/Attestor/__Libraries/StellaOps.Attestor.ProofChain/Predicates/ReachabilitySubgraphPredicate.cs` -- predicate for attested reachability subgraphs (slices).
+- **Reachability Subgraph Statement**: `Statements/ReachabilitySubgraphStatement.cs` -- in-toto statement wrapping the subgraph slice.
+- **Proof Graph Service**: `Graph/InMemoryProofGraphService.cs` (with `.Queries`, `.Subgraph`) -- graph service supporting subgraph extraction (slice).
+- **Graph Path**: `Graph/ProofGraphPath.cs` -- path through the reachability graph.
+- **Graph Subgraph**: `Graph/ProofGraphSubgraph.cs` -- extracted minimal subgraph.
+- **Replay Manifest**: `Replay/AIArtifactReplayManifest.cs` -- manifest for deterministic replay of reachability analysis.
+- **Replay Result**: `Replay/ReplayResult.cs` -- result of replaying a reachability analysis.
+- **Replay Verification**: `Replay/ReplayVerificationResult.cs` -- verification of replay fidelity.
+- **Replay Status**: `Replay/ReplayStatus.cs` -- enum tracking replay outcome.
+- **Replay Input Artifact**: `Replay/ReplayInputArtifact.cs` -- input artifact for replay (graph data, configuration).
+- **Witness Payload**: `Statements/ReachabilityWitnessPayload.cs` (with `.Path`) -- witness data for reachability paths.
+- **REST API**: `StellaOps.Attestor.WebService/Controllers/ChainController.cs` -- API for querying reachability chains.
+- **Tests**: `__Tests/StellaOps.Attestor.ProofChain.Tests/ReachabilitySubgraphTests.cs`
+
+## E2E Test Plan
+- [ ] Extract a reachability slice from a proof graph via `InMemoryProofGraphService.Subgraph` and verify the minimal subgraph
+- [ ] Build a `ReachabilitySubgraphPredicate` from the extracted slice and sign it into a DSSE envelope
+- [ ] Replay a reachability analysis via `AIArtifactReplayManifest` and verify `ReplayResult` matches the original
+- [ ] Verify replay fidelity via `ReplayVerificationResult` and confirm the replayed graph matches the original
+- [ ] Query a reachability chain via `ChainController` REST API and verify the response contains path data
+- [ ] Store a reachability subgraph attestation and retrieve it by subject digest
+- [ ] Create `ReplayInputArtifact` entries for a reachability analysis and verify all inputs are captured for replay