Map-reduce summarization with reranking for long docs

Workflow: 1) Chunk: Split by headings; keep semantic boundaries. 2) Map: Summarize each chunk with strict key points; include IDs. 3) Rerank: Select top N mapped summaries by relevance to the query. 4) Reduce: Merge into a coherent summary; maintain sections and citations. 5) Validate: Check for contradictions; prefer direct quotes for contentious claims. 6) Evaluate: Human review on samples; track coverage and faithfulness. Result: Scales to book-length docs with controllable quality.