Add Phase 8.3 ExplainAPI wiki page (90th page) - build_explain_app() FastAPI factory + 9 REST routes - APIKeyAuth (dependency injection) + TokenBucket (per-key rate limit) - Pydantic v2 response models (TraceResponse, GraphSnapshotResponse, etc.) - CognitiveCycle sidecar integration pattern - 5 Prometheus metrics + PromQL examples - 12 test targets (httpx.ASGITransport) - 12-step impl order - Phase 8 roadmap table - _Sidebar.md: Phase 8 section now 3 links