chore(rag): add eval knowledge base mirror

knowledge_base/rag-eval/rag/rag-chunk-context-reconstruction.md

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+---
+title: RAG Chunk Context Reconstruction
+keywords: [split into multiple chunks, retrieval context, neighbor chunk, same section, breadcrumb context]
+summary: Preserve context when long RAG sections are split into multiple retrievable chunks.
+category: rag
+source: rag-chunk-context-reconstruction
+breadcrumb: RAG > Chunking > Context Reconstruction
+kb_scope: rag-eval
+covers: [rag chunking, context packing, breadcrumbs]
+when_to_retrieve: Use when a retrieval question asks how to preserve context across split chunks.
+---
+
+# RAG
+
+## Chunking
+
+### Context Reconstruction
+
+When a long section is split into multiple chunks, retrieval should keep enough local structure for the answer.
+
+Recommended behavior:
+
+1. Store the breadcrumb with every chunk.
+2. Preserve the same section identity across adjacent chunks.
+3. During context packing, include a neighbor chunk when the selected chunk depends on nearby setup or definitions.
+4. Prefer concise evidence blocks that show the breadcrumb and the relevant content span.
+
+The key concepts are neighbor chunk, same section, and breadcrumb.