Usage telemetry: sendInteractions endpoint

[maxine-at-forecast]

Summary

Implement sendInteractions — a fire-and-forget procedure for clients to report download, citation, and derivative usage events. Enables popularity-based discovery ranking.

Background

From the original XRPC design (forecast-bio/atdata#49):

• Input: interactions[] — array of {type: "download"|"citation"|"derivative", datasetUri, timestamp}
• Output: empty (fire-and-forget)
• Analogous to Bluesky's sendInteractions for feed engagement signals

Design Considerations

• Privacy: Need opt-in/anonymization design before implementing
• Storage: Append-only event log vs aggregated counters
• Ranking: How interaction counts feed into searchDatasets relevance scoring

Tasks

• Design privacy model (opt-in, anonymization, retention policy)
• Define science.alt.dataset.sendInteractions lexicon in atdata-lexicon
• Implement endpoint in atdata-app
• Wire interaction counts into search ranking

Related

• Closed: Design XRPC query and procedure lexicons for ac.foundation.dataset AppView atdata#49 (XRPC lexicon design — listed as deferred)
• Existing: getAnalytics and getEntryStats endpoints (server-side view counting already exists)