Classroom presence should be an expiring lease, not a socket fact

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Online classroom and shared workspace designs should issue short-lived RTC tokens from a versioned contract and treat presence as an expiring claim. A lease-based model, renewed by heartbeats, bounds how wrong the 'online' status can be, so a user who closed a laptop does not appear online indefinitely. The article compares this with room membership events and client-pushed status, noting the simpler options suit cases where accuracy is not a promise to users. It recommends a shared envelope with explicit identity, room, role, and freshness fields, with server-owned timestamps in UTC. A session epoch, checked with compare-and-swap, prevents delayed disconnect events from older tabs from overwriting newer presence records.

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