semi implemented and features implemented save checkpoint

docs/features/unchecked/graph/graph-explorer-api-with-streaming-tiles.md

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+# Graph Explorer API with Streaming Tiles
+
+## Module
+Graph
+
+## Status
+IMPLEMENTED
+
+## Description
+Graph query and visualization API providing streaming tile-based graph rendering, path queries, diff computation between graph revisions, RBAC-enforced exports (SVG/PNG/GraphML), and overlay support for policy/VEX/reachability annotations.
+
+## Implementation Details
+- **API program**: `src/Graph/StellaOps.Graph.Api/Program.cs` -- minimal API endpoints for graph queries, diffs, exports, search, paths, lineage, overlays
+- **Query service**: `src/Graph/StellaOps.Graph.Api/Services/IGraphQueryService.cs`, `InMemoryGraphQueryService.cs` -- graph node/edge query
+- **Search service**: `src/Graph/StellaOps.Graph.Api/Services/IGraphSearchService.cs`, `InMemoryGraphSearchService.cs` -- full-text graph search
+- **Path service**: `src/Graph/StellaOps.Graph.Api/Services/IGraphPathService.cs`, `InMemoryGraphPathService.cs` -- graph path traversal
+- **Diff service**: `src/Graph/StellaOps.Graph.Api/Services/IGraphDiffService.cs`, `InMemoryGraphDiffService.cs` -- diff computation between graph revisions
+- **Export service**: `src/Graph/StellaOps.Graph.Api/Services/IGraphExportService.cs`, `InMemoryGraphExportService.cs` -- RBAC-enforced export (SVG/PNG/GraphML)
+- **Lineage service**: `src/Graph/StellaOps.Graph.Api/Services/IGraphLineageService.cs`, `InMemoryGraphLineageService.cs` -- lineage traversal
+- **Overlay service**: `src/Graph/StellaOps.Graph.Api/Services/IOverlayService.cs`, `InMemoryOverlayService.cs` -- policy/VEX/reachability overlays
+- **Reachability delta**: `src/Graph/StellaOps.Graph.Api/Services/IReachabilityDeltaService.cs`, `InMemoryReachabilityDeltaService.cs` -- reachability delta computation
+- **Rate limiting**: `src/Graph/StellaOps.Graph.Api/Services/RateLimiterService.cs` -- API rate limiting
+- **Metrics**: `src/Graph/StellaOps.Graph.Api/Services/GraphMetrics.cs` -- Prometheus-compatible API metrics
+- **Audit**: `src/Graph/StellaOps.Graph.Api/Services/IAuditLogger.cs` -- audit logging for graph access
+- **Contracts**: `src/Graph/StellaOps.Graph.Api/Contracts/SearchContracts.cs`, `LineageContracts.cs`, `ReachabilityContracts.cs`
+- **Tests**: `src/Graph/__Tests/StellaOps.Graph.Api.Tests/` -- QueryServiceTests, SearchServiceTests, PathServiceTests, DiffServiceTests, ExportServiceTests, LineageServiceTests, LoadTests, MetricsTests, RateLimiterServiceTests, GraphApiContractTests
+- **Source**: SPRINT_0207_0001_0001_graph.md
+
+## E2E Test Plan
+- [ ] Verify graph query API returns nodes and edges for given criteria
+- [ ] Test streaming tile rendering for large graphs
+- [ ] Verify diff computation between two graph revisions
+- [ ] Test RBAC-enforced export in SVG/PNG/GraphML formats
+- [ ] Verify overlay annotations for policy/VEX/reachability layers
+- [ ] Test search API returns relevant results with ranking