drainShardEvents only exits via ctx cancellation for an idle subscription
— that's the steady-state when all replayed events are already past.
Saving the cursor with the canceled passCtx silently drops every
advance, so the next pass re-subscribes from the same floor and
re-replays the same events. Symptom in s3tests: status=error shards=16
errors=16 on every pass, and 1/6 expire3/* dispatches lost to a race
between concurrent shard drains all retrying the same events.
Use a 5s timeout derived from context.Background for the save, and
treat passCtx Deadline/Canceled from drain as a clean end-of-pass —
not a shard-level error to log.
Chris Lu
bfea01e113