* docs(events): document durable thread seq watermark
RUN_EVENT_STREAM.md described seq as monotonic but did not cover the durable per-thread high-water mark that keeps allocations monotonic after a run is deleted. Record that behavior in the Record Envelope section, including that thread deletion drops the mark only when no events remain.
* test(scheduler): pin clock for scheduled-run timezone assertions
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Co-authored-by: yu1128-L <296164533+yu1128-L@users.noreply.github.com>
Co-authored-by: Willem Jiang <willem.jiang@gmail.com>