test: add rag retrieval baseline

eval/rag-retrieval/fixtures/chat-rag-chunk-context.json

@@ -0,0 +1,25 @@
+{
+  "caseId": "chat-rag-chunk-context",
+  "query": "If a long section is split into multiple chunks, how do we keep retrieval context?",
+  "retrievedAt": "2026-07-05T00:00:00Z",
+  "candidates": [
+    {
+      "rank": 1,
+      "docId": "rag-chunk-context-reconstruction",
+      "title": "RAG Chunk Context Reconstruction",
+      "breadcrumb": "RAG > Chunking > Context Reconstruction",
+      "content": "After a chunk hit, expand to neighbor chunk candidates from the same section and preserve breadcrumb metadata in the evidence pack.",
+      "score": 0.79,
+      "retrievalLayer": "L1"
+    },
+    {
+      "rank": 2,
+      "docId": "rag-breadcrumb-embedding-gap",
+      "title": "RAG Breadcrumb Embedding Gap",
+      "breadcrumb": "RAG > Embedding > Breadcrumb",
+      "content": "Embedding title and breadcrumb with content helps recover section semantics.",
+      "score": 0.72,
+      "retrievalLayer": "L1"
+    }
+  ]
+}