Phase 3: Hybrid Retrieval - HybridRetriever: TF-IDF prefilter + semantic rerank + RRF fusion - WikiScopedFilter: BFS wiki-graph traversal - RetrievalRoute: Direct | WikiScoped | ReferenceOnly - 10 unit tests Phase 4: LLM Call Optimization - ChunkOptimizer: unified pipeline (threshold + budget + dedup) - ScoreThresholdFilter: configurable min_score (default 0.6) - BudgetSelector: greedy selection within byte budget - ShingleDeduplicator: Jaccard similarity dedup - 8 unit tests QueryRouter (Phase 3+4 Integration) - Bridges WikiLinkGraph + HybridRetriever + ChunkOptimizer - RouterConfig: max_hops, thresholds, budget, RRF weights - WikiGraphBuilder: construct graph from markdown docs - 11 unit tests Integration Tests (it_phase3_phase4.rs) - 19 end-to-end tests covering full pipeline - Wiki-link parsing, graph traversal, route selection - TF-IDF prefilter, RRF fusion, chunk optimization - Edge cases (empty, no matches, config customization) Total: 107 tests passing (was 32)