feat(rag): dense+BM25 hybrid on MilvusClientV2, drop SDK path

Replace legacy MilvusServiceClient knowledge search/write with a single
MilvusClientV2 hybrid store (BM25 function + dense ANN + RRFRanker).
Use collection biz_hybrid and require knowledge reindex.

devflow/index.md

@@ -12,6 +12,7 @@
 | 日期 | slug | 说明 | 领域 | 关键词 | 关联 OpenSpec | 状态 |
 |---|---|---|---|---|---|---|
 | 2026-07-27 | rag-chunk-evidence-identity-dedup | chunk 级证据身份、去重、retrieve-k/return-n 与 SearchPort 地基，为 hybrid 铺路。 | RAG/证据身份/去重 | evidenceKey, maxChunksPerDocument, retrieve-k, return-n, KnowledgeSearchPort, document_id chunk-scoped | openspec/changes/archive/2026-07-27-rag-chunk-evidence-identity-dedup | archived |
+| 2026-07-27 | rag-bm25-hybrid-drop-sdk | 真 dense+BM25 hybrid（MilvusClientV2），废弃知识路径旧 SDK 检索/写入。 | RAG/BM25/hybrid | MilvusClientV2, BM25, hybridSearch, RRFRanker, biz_hybrid, drop SDK path | openspec/changes/archive/2026-07-27-rag-bm25-hybrid-drop-sdk | archived |
 | 2026-07-27 | rag-hybrid-search-rrf | Delivery 2：可配置 hybrid 检索与 RRF 多路融合（不绑旧 SDK）。 | RAG/hybrid/RRF | hybrid mode, RRF, KnowledgeSearchPort, filtered+unfiltered fusion, sparse-lite lexical | openspec/changes/archive/2026-07-27-rag-hybrid-search-rrf | archived |
 | 2026-07-21 | single-react-tool-invocation-store | 建立统一 ToolBoundary 与 Redis canonical invocation store，集中生命周期、证据状态、TTL、容量和 Run 所有权。 | Harness/Tool boundary/Canonical store | ISS-014, ToolBoundary, canonical invocation, PROJECTING, READY, ERROR, TTL, RESULT_TOO_LARGE | openspec/changes/archive/2026-07-21-single-react-tool-invocation-store | archived |
 | 2026-07-21 | single-react-harness-run-context | 建立显式 RunContext、Harness Core、预算、取消、类型化重试和 Tool Store 基础。 | Harness/Run lifecycle/Budget | ISS-014, RunContext, deadline, cancellation, budget, retry, ToolCallKey | openspec/changes/archive/2026-07-21-single-react-harness-run-context | archived |

devflow/projects/2026-07-27-rag-bm25-hybrid-drop-sdk/acceptance.md

@@ -0,0 +1,22 @@
+# Acceptance
+
+## Done
+
+- `MilvusHybridKnowledgeStore`: schema BM25 function + dense, hybridSearch+RRFRanker, dense search
+- `VectorSearchService` only routes dense|hybrid to V2 store
+- `VectorIndexService` writes via V2 store
+- Removed knowledge-path `MilvusServiceClient` bean wiring
+- Config: `milvus.collection=biz_hybrid`, `retrieval.search.mode=hybrid`
+
+## Tests
+
+```text
+mvn -Dtest=LookupKnowledgeToolTest,KnowledgeEvidencePostProcessorTest,RagResultProjectorTest,RrfFusionTest,VectorKnowledgeSearchAdapterHybridTest,VectorSearchServiceTest,VectorIndexServiceTest test
+```
+
+EXIT:0
+
+## Ops note
+
+Reindex all knowledge docs into `biz_hybrid` before production hybrid search is meaningful.
+Legacy `biz` collection is unused by knowledge path.

devflow/projects/2026-07-27-rag-bm25-hybrid-drop-sdk/brief.md

@@ -0,0 +1,3 @@
+# Brief: rag-bm25-hybrid-drop-sdk
+
+True dense+BM25 hybrid on a single MilvusClientV2 backend. Legacy SDK search/write for knowledge path removed. New collection `biz_hybrid` requires reindex.

devflow/projects/2026-07-27-rag-bm25-hybrid-drop-sdk/decisions.md

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+# Decisions
+
+- Single backend: MilvusClientV2 only for knowledge RAG
+- Drop sdk/spring/auto retrieval routing
+- New collection biz_hybrid to avoid mutating legacy biz schema in place
+- Hybrid = dense ANN + BM25 sparse ANN + RRFRanker
+- Dense L2 enrichment for threshold compatibility on hybrid hits