D244 — server-side importance and communities

Decision. The server computes a global PageRank (directed, damping 0.85, dangling mass spread uniformly) and a community partition (Louvain in node order, no randomness, then every community split into its connected components) on the graph of the concepts the caller can see, before scope and limit. The graph snapshot carries pagerank and community per node and the ordered communities list; past its limits it keeps the most important nodes and edges instead of the first ids. The Atlas colours by the server's communities and no longer runs Louvain. atlas_overview(structure: true) lists the most central concepts and the main communities for agents. This amends D226's truncation rule and settles D234's note that any reduction for a large KB happens on the server.

Why. Truncation by id dropped an alphabetical tail of the KB however central it was, and communities computed in the browser on the returned snapshot recoloured a scoped or truncated view and were invisible to agents. Computing both once, on the visible graph, fixes the three at once, and computing them on the visible graph keeps D226's rule that the numbers disclose no hidden concept. The cost is a PageRank and a Louvain run per snapshot request, which at the 5,000-node ceiling is milliseconds.

Alternatives rejected. - Full Leiden: its guarantee that no community is disconnected is what matters, and splitting Louvain's communities into components gives it for a fraction of the code; Leiden's speed advantage is irrelevant at ≤ 5k nodes. - Keep Louvain in the browser: the recolouring of scoped views and the agent-blind structure would stay. - Structure on every atlas_overview: the tool opens most sessions, and ~25 extra lines per call is context nobody asked for.

Consequences. The ranking, anchor and slot rules of the old communities.ts (size, then smallest member; anchor by degree, then id; twelve hues, the rest slot 0) now live in graphalgo.Communities and must stay there. The UI does not use pagerank yet: node size and list order are still by degree. Dropping graphology and graphology-communities-louvain shrank the gzipped bundle from 306.8 KiB to 287.0 KiB.