Build and maintain a topic graph over your agent session history. Reads every Claude session transcript plus the pruned sessions that survive only in history.jsonl, clusters them by topic using local TF-IDF (no API calls, no embeddings), and writes an interactive graph you can open in a browser. Use when the user says "/session-brain", "build my session map", "cluster my claude sessions", "map my session history", "rebuild the session graph", "show me my session graph", "what have I been working on lately", "what topics have gone stale". Different from wiki-history-ingest, which distils sessions into vault pages: this builds a retrieval index over the raw sessions and never writes to the vault.