The stale-event check excluded heartbeats from lastActiveEventAt, so a
quiet-but-connected session (only receiving heartbeats) tripped the 20s
stale timer and triggered a full resync every ~15s. This re-fetched
listPendingQuestions, listPendingPermissions, session.get, and
session.messages despite the event stream being healthy.
Track all stream activity (including heartbeats) in a global
lastStreamActivityAt ref. The stale check now only fires when no events
at all arrive for 20s, meaning the stream is genuinely dead.
Resyncs still fire correctly on genuine reconnects, transport switches,
and status-poll escalation when a real discrepancy is detected.
Fixes#1656
Tom Rochette
8f2e058b27