mnem-graphrag

GraphRAG primitives for mnem.

Scope (E4 T2)

Extractive community summarization: Centroid + MMR.

• Score(s_i) = alpha * cos(s_i, centroid) + beta * cos(s_i, query) + gamma * centrality(i)
• Diversity via MMR with tunable lambda.
• No LLM, no BM25, no new heavy deps.
• Reuses the existing mnem-embed-providers::Embedder trait.

Non-goals (this crate, this turn)

• Leiden communities (E1 will add community::leiden in a separate turn).
• Personalized PageRank (E2 will replace the degree-centrality fallback).
• Abstractive summarization (explicitly forbidden: no LLM in this path).