The test built the buffer with the real DateTime.UtcNow clock but emitted
an event with the file's fixed EvtTime timestamp (2026-06-23). As real
time drifted more than the 1h window past that fixed timestamp, the
just-appended record was evicted inside the same Append call, before
Snapshot() ran. BroadcastLogSink.Emit itself buffers unconditionally
regardless of attach state, so this was a test bug, not a sink bug. Pin
the buffer's clock to EvtTime, matching every sibling test's NewSink setup.
mika kuns
58f8b11dbb