Co-authorship edge graph for a set of authors (TOOL-01).

For each input author, returns outgoing edges to every co-author on papers published within the time window. Edges are deterministic and derived from the paper_authors join table — not from any cached graph snapshot.

Returns asymmetric (from, to) edges, sorted by papers_count DESC; capped at 500 edges per request. Useful for downstream reviewer-triage and collaboration-neighborhood workflows.

Note: this surfaces the FULL co-author neighborhood per input author. If a symmetric subgraph restricted to {input_authors} is needed, filter the returned edges client-side (YAGNI — not implemented server-side).

Rate limit: 20/minute per API key.